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## Texas Go Math Grade 4 Lesson 8.2 Answer Key Estimate Products

**Essential Question**

What strategies can you use to estimate products?

Answer:

There are two methods are there we can use to estimate the product

i) Mental Math Multiplication Method

ii) Place value multiplication method

**Unlock the Problem**

• Underline any information you will need.

The Smith family opens the door of their refrigerator 32 times in one day. There are 31 days in May. About how many times is it opened in May?

Answer:

992 times

Explanation:

opens the door of their refrigerator 32 times in one day.

There are 31 days in May.

to know how many times is it opened in May

32 x 31

STEP 1 Find half of 32 by dividing by 2

32 /2 = 16

STEP 2 Multiply

16 x 31 = 403

STEP 3 double the 403

2 x 403 = 992

**One Way** Use rounding and mental math.

**Estimate. 32 × 31**

STEP 1 Round each factor

STEP 2 Use mental math.

3 × 3 = 9 ← basic fact

30 × 30 = _________

Answer: 900

Explanation:

Round each factor

30 x 30

3 x 3 x 10 x 10

9 x 100 = 900 times

So, the Smith family opens the refrigerator door about 900 times during the month of May.

All 24 light bulbs in the Park family’s home are CFL light bulbs. Each CFL light bulb uses 28 watts to produce light. About how many watts will the light bulbs use when turned on all at the same time?

Answer:

672 watts

Explanation:

All 24 light bulbs in the Park family’s home are CFL light bulbs.

Each CFL light bulb uses 28 watts to produce light

24 x 28 = 672 watts

**Another Way** Use mental math and compatible numbers.

**Compatible numbers are numbers that are easy to compute mentally.**

Estimate. 24 × 28

STEP 1 Use compatible numbers.

Answer: 750

Explanation:

25 x 3 x 10

75 x 10 = 750

STEP 2 Use mental math.

25 × 3 = 75

25 × 30 = __________

Answer:

25 x 30 = 750

STEP 2 Use mental math.

25 × 3 = 9 ← basic fact

25 × 30 = 750

So, about 750 watts are used.

Explanation:

To estimate the product, we first round off the multiplier and the multiplicand to the nearest tens, hundreds, or thousands and then multiply the rounded numbers.

**Try This!** Estimate 26 × $79.

(A) Round to the nearest ten

26 × $79 is about ____________ .

Answer:

26 × $79 is about $2,054

Explanation:

In order to estimate products, we round the given factors to the required place value. Estimating products help us to check the reasonableness of an answer.

(B) Compatible numbers

26 × $79 is about ____________ .

Answer:

26 × $79 is about $2,054

Explanation:

Compatible numbers are pairs of numbers that are easy to multiply, mentally.

The numbers 26 and 79 are not compatible for multiplication since the product 2,054 can’t be easily calculated mentally.

To estimate 26 × 79, replace 26 and 79 with the compatible numbers 25 and 80.

**Share and Show**

Question 1.

To estimate the product of 62 and 28 by rounding, how would you round the factors? What would the estimated product be?

Answer:

62 x 28 = 1736

Explanation:

62 is estimated number is 60 and 28 is 30

the product is 1800

1736 is estimated as 1800

**Estimate the product. Choose a method.**

Question 2.

96 × 34

Answer: 3,264

Estimate: 3000

Explanation:

In order to estimate products, we round the given factors to the required place value. Estimating products help us to check the reasonableness of an answer.

Question 3.

47 × $39

Answer: 1,833

Estimate: 1800

Explanation:

In order to estimate products, we round the given factors to the required place value. Estimating products help us to check the reasonableness of an answer.

Question 4.

78 × 72

Answer: 5,616

Estimate: 5600

Explanation:

In order to estimate products, we round the given factors to the required place value. Estimating products help us to check the reasonableness of an answer.

**Math Talk**

Mathematical Processes

Describe how you know if an estimated product will be greater than or less than the exact answer.

Answer:

The difference to be checked between the estimated product and the exact values product.

If then the estimated product will be checked for greater than or less than the exact.

**Problem Solving**

Practice: Copy and Solve Estimate the product. Choose a method.

Question 5.

61 × 31

Answer: 1,891

Estimated

60 x 30 = 1800

Explanation:

In order to estimate products, we round the given factors to the required place value. Estimating products help us to check the reasonableness of an answer.

Question 6.

52 × 68

Answer: 3,536

50 x 70 = 3500

Explanation:

In order to estimate products, we round the given factors to the nearest place value.

Estimating products help us to check the reasonableness of an answer.

Question 7.

26 × 44

Answer: 1,144

25 x 45 = 1,125

Estimate: 1100

Explanation:

In order to estimate products, we round the given factors to the nearest place value.

Estimating products help us to check the reasonableness of an answer.

Question 8.

57 × $69

Answer: 3,933

Estimate:55 x 70=3850

Explanation:

In order to estimate products, we round the given factors to the nearest place value.

Estimating products help us to check the reasonableness of an answer.

Question 9.

55 × 39

Answer: 2,145

Estimate: 55 x 40 = 2200

Explanation:

In order to estimate products, we round the given factors to the nearest place value.

Estimating products help us to check the reasonableness of an answer.

Question 10.

51 × 81

Answer: 4,131

Estimate: 50 x 80 = 4000

Explanation:

In order to estimate products, we round the given factors to the nearest place value.

Estimating products help us to check the reasonableness of an answer.

Question 11.

47 × $32

Answer: 1,504

Estimate: 45 x 30 = 1350

Explanation:

In order to estimate products, we round the given factors to the nearest place value.

Estimating products help us to check the reasonableness of an answer.

Question 12.

49 × 64

Answer: 3,136

Estimate:50 x 60 =3000

Explanation:

In order to estimate products, we round the given factors to the nearest place value.

Estimating products help us to check the reasonableness of an answer.

**H.O.T.** Find two possible

Explanation:

In order to estimate products, we round the given factors to the nearest place value.

Estimating products help us to check the reasonableness of an answer.

**Find the two possible factors for the estimated products.**

Question 13.

2,800

Answer:

140 x 20

Explanation:

To estimate the product, we first round off the multiplier and the multiplicand to the nearest tens, hundreds, or thousands and then multiply the rounded numbers.

A factor is a number that divides into another number exactly without leaving a remainder.

(14 x 2)(10 x 10)

140 x 20 = 2800

140 x 20

Question 14.

8,100

Answer:

90 x 90

Explanation:

To estimate the product, we first round off the multiplier and the multiplicand to the nearest tens, hundreds, or thousands and then multiply the rounded numbers.

A factor is a number that divides into another number exactly without leaving a remainder.

(9x 9)(10 x 10)

81 x 100 = 8,100

90 x 90

Question 15.

5,600

Answer:

70 x 80

Explanation:

To estimate the product, we first round off the multiplier and the multiplicand to the nearest tens, hundreds, or thousands and then multiply the rounded numbers.

A factor is a number that divides into another number exactly without leaving a remainder.

(7 x 8)(10 x 10)

56 x 100 = 5600

70 x 80

Question 16.

2,400

Answer:

120 x 20

Explanation:

To estimate the product, we first round off the multiplier and the multiplicand to the nearest tens, hundreds, or thousands and then multiply the rounded numbers.

A factor is a number that divides into another number exactly without leaving a remainder.

(12 x 2)(10 x 10)

24 x 100 = 2400

120 x 20

Question 17.

Apply On average, a refrigerator door is opened 38 times – each day. Len has two refrigerators in his house. Based on this average, about how many times in a 3-week period are the refrigerator doors opened?

Answer:

228 times

Apply On average, a refrigerator door is opened 38 times – each day.

Len has two refrigerators in his house.

Based on this average, number of times in a 3-week period are the refrigerator doors opened

38 x 2 x 3

38 x 6 = 228 times

Question 18.

The cost to run a refrigerator is about $57 each year. About how much will it have cost to run by the time it is 15 years old?

Answer: $ 855

Explanation:

The cost to run a refrigerator is about $57 each year.

Total cost to run by the time in 15 years old

57 x 15 = $855

Question 19.

**H.O.T. Multi-Step** If Mel opens his refrigerator door 36 times every day, about how many times will it be opened in April? Will the exact answer be more than or less than the estimate? Explain.

Answer:

1080 times

Estimate: 1000 times

Explanation:

If Mel opens his refrigerator door 36 times every day,

In April month there are 30 days

So, 30 x 36= 1080 times

1080 is more than the exact answer.

Question 20.

**H.O.T.** Explain why $2,400 and $2,000 are both reasonable estimates for problems A and B below Try This! on page 274.

Answer:

Both are correct as they are the estimates.

Explanation:

In order to estimate products, we round the given factors to the required place value.

Estimating products help us to check the reasonableness of an answer.

Question 21.

**H.O.T.** What’s the Question? The estimated product of two numbers, that are not multiples of ten, is 2,800.

Answer:

**Daily Assessment Task**

**Fill in the bubble completely to show your answer.**

Question 22.

A scientist watches a thorny dragon eat ants for 32 minutes. It eats at a rate of up to 45 ants every minute. At this rate, about how many ants does the thorny dragon eat in 32 minutes?

(A) 2,000 ants

(B) 1,500 ants

(C) 1,600 ants

(D) 150 ants

Answer:

Option(B)

Explanation:

A scientist watches a thorny dragon eat ants for 32 minutes.

It eats at a rate of up to 45 ants every minute.

Number of ants eaten by the thorny dragon in 32 minutes

Estimates of 32 is 30 and 45 is 50

So, 30 x 50 = 1500

Question 23.

Denise uses 24 beads to make 1 beaded necklace. About how many beads does she need to make 42 beaded necklaces?

(A) 1,500 beads

(B) 100 beads

(C) 800 beads

(D) 150 beads

Answer:

Option(C)

Explanation:

Denise uses 24 beads to make 1 beaded necklace.

Number of beads she need to make 42 beaded necklaces

Estimate of 24 is 20 and 42 is 40

So, compatible pairs 20 x 40 = 800

Question 24.

**Multi-Step** Mr. Parker jogs for 35 minutes each day. He jogs 5 days in week 1, 6 days in week 2, and 7 days in week 3. About how many minutes does he jog?

(A) 400 minutes

(§) 350 minutes

(C) 200 minutes

(D) 800 minutes

Answer:

Option(D)

Explanation:

Mr. Parker jogs for 35 minutes each day.

He jogs 5 days in week 1, = 5 x 35 =175 minutes

6 days in week 2, 35 x 6 = 210 minutes

and 7 days in week 3, 7 x 35 = 245

Total minutes he jogs = 175 + 210 + 245 = 630

Nearest estimate: 800

**TEXAS Test Prep**

Question 25.

Which is the best estimate for the product 75 × 23?

(A) 2,600

(B) 2,200

(C) 160

(D) 1,600

Answer:

Option(D)

Explanation:

23 x 75 = 1725

Estimate of 23 is 20 and 75 is 80

So, 20 x 80 = 1600

### Texas Go Math Grade 4 Lesson 8.2 Homework and Practice Answer Key

**Estimate the product. Choose a method.**

Question 1.

42 × 28

Answer:

Estimate:1200

Explanation:

Compatible numbers, these are a pair of numbers used in multiplication to estimate the product.

Estimates of 42 is 40 and 28 is 30.

So, compatible pairs are

40 x 30 =1200

Question 2.

95 × 33

Answer:

Estimate: 3000

Explanation:

Compatible numbers, these are a pair of numbers used in multiplication to estimate the product.

Estimate of 95 is 100 nd 33 is 30

So, compatible pairs are

100 x 30 = 3000

Question 3.

61 × 58

Answer:

Estimate: 1200

Explanation:

Compatible numbers, these are a pair of numbers used in multiplication to estimate the product.

Estimate of 61 is 60 and 58 is 60

So, compatible pairs are

60 x 60 = 1200

Question 4.

77 × 13

Answer:

Estimate: 800

Explanation:

Compatible numbers, these are a pair of numbers used in multiplication to estimate the product.

Estimate of 77 is 80 and 13 is 10

Compatible pairs are 80 x 10 = 800

**Find two possible factors for the estimated product.**

Question 5.

1,600

Answer:

40 x 40

Explanation:

Factors are the numbers that divide the numbers exactly with a remainder zero.

So, 40 is the factor of estimated product.

Question 6.

4,500

Answer:

90 x 50

Explanation:

Factors are the numbers that divide the numbers exactly with a remainder zero.

So, 90 and 50 are the factor of estimated product.

Question 7.

6,000

Answer:

60 x 100

Explanation:

Factors are the numbers that divide the numbers exactly with a remainder zero.

So, 60 and 100 are the factor of estimated product.

Question 8.

3,200

Answer:

80 x 40

Explanation:

Factors are the numbers that divide the numbers exactly with a remainder zero.

So, 80 and 40 are the factor of estimated product

**Problem Solving**

Question 9.

A bus holds 58 people. For the last away game, 27 bus loads of fans traveled to the game. About how many fans went to the game on the buses?

Answer:

58 x 27 = 1566

Explanation:

A bus holds 58 people.

For the last away game, 27 bus loads of fans traveled to the game.

Number of fans went to the game on the buses

58 x 27 = 1566

Question 10.

The fence posts along Tom’s driveway are 96 inches apart. There are 32 fence posts, About how many inches long is the fence?

Answer:

96 x 32 = 3072

Explanation:

The fence posts along Tom’s driveway are 96 inches apart.

There are 32 fence posts,

Number of inches long is the fence 96 x 32 = 3072

Question 11.

Will the exact answer to Problem 9 be more than or less than the estimate? Explain.

Answer:

The exact answer to Problem 9 is less than the estimate.

Explanation:

The answer for question number 9 is 1566

Estimate of 1566 is 1600

Question 12.

Nona used compatible numbers to estimate that 25 × 42 is about 1,000. Gerry rounded and estimated that the product is about 1,200. Which estimate is closest to the exact answer? Explain.

Answer:

Gerry estimate is closest to the exact answer.

Explanation:

Nona used compatible numbers to estimate that 25 × 42 is about 1,000.

Gerry rounded and estimated that the product is about 1,200.

Gerry rounded the compatible pairs as 30 x 40 = 1200

Gerry estimate is closest to the exact answer.

**Fill in the bubble completely to show your answer.**

Question 13.

Which is the best estimate for the product of 26 × 78?

(A) 2,400

(B) 1,600

(C) 2,000

(D) 1,400

Answer:

Option(A)

Explanation:

26 x 78 = 2028

Estimate of 26 is 30 and 78 is 80

So, 30 x 80 = 2400

Question 14.

For which two factors is the product closest to 4,800?

(A) 24 × 24

(B) 56 × 83

(C) 47 × 66

(D) 92 × 38

Answer:

Option(B)

Explanation:

Estimate of 56 is 60 and 83 is 80

60 x 80 = 4800

Question 15.

A store has 12 rows of eye glasses in a display. There are 27 pairs of glasses in each row. Which estimate is closest to the number of pairs of glasses in the store’s display?

(A) 300

(B) 240

(C) 360

(D) 200

Answer:

Option(A)

Explanation:

A store has 12 rows of eye glasses in a display.

There are 27 pairs of glasses in each row.

12 x 27 = 324

Estimate 300 is closest to the number of pairs of glasses in the store’s display.

Question 16.

A factory uses 28 screws for each bookcase they make. In one day, they produce 44 bookcases. About how many screws are needed each day?

(A) 1,500

(B) 1,000

(C) 800

(D) 1,200

Answer:

Option(D)

Explanation:

A factory uses 28 screws for each bookcase they make.

In one day, they produce 44 bookcases.

28 x 44 = 1232

Number of screws needed each day 1200

Estimate of 28 is 30 and 44 is 40

40 x 30 = 1200

Question 17.

**Multi-Step** A theater has 17 rows of seats on the floor and 11 rows of seats in the balcony. There are 55 seats in each row. Which is the best estimate of the total number of seats in the theater?

(A) 180

(B) 1,500

(C) 2,400

(D) 1,800

Answer:

Option(B)

Explanation:

A theater has 17 rows of seats on the floor and

11 rows of seats in the balcony.

There are 55 seats in each row.

(17 + 11) x 55 = 1540

The best estimate of the total number of seats in the theater is 1500

Question 18.

**Multi-Step** There are 48 beads in a package. Mariah bought 4 packages of blue, 9 packages of gold, 6 packages of red, and 2 packages of silver beads. Which is the best estimate of the total number of beads she bought?

(A) 1,000

(B) 800

(C) 1,200

(D) 2,400

Answer:

Option(A)

Explanation:

There are 48 beads in a package.

Mariah bought 4 packages of blue, 9 packages of gold, 6 packages of red, and 2 packages of silver beads. 48 x (4+9+6+2) = 1008

The best estimate of the total number of beads she bought are 1000.