Practice the problems of Math in Focus Grade 2 Workbook Answer Key Chapter 10 Mental Math and Estimation to score better marks in the exam.

## Math in Focus Grade 2 Chapter 10 Answer Key Mental Math and Estimation

**Chapter Review/Test**

**Vocabulary**

**Fill in the blanks with words from the box.**

Question 1.

You can use an estimate to check that a sum is __________

Question 2.

86 is 90 when rounded to the _____.

Answer:

Question 3.

Add to find the ____________ of two or more numbers.

Answer:

Question 4.

Subtract to find the ____________ between two or more numbers.

Answer:

**Concepts and Skills Add mentally.**

Question 5.

325 + 9 = _______

Answer: 334

Question 6.

436 + 20 = _______

Answer: 456

Question 7.

691 + 70 = _______

Answer: 761

Question 8.

635 + 300 = _______

Answer: 935

**Subtract mentally.**

Question 9.

541 – 5 = _______

Answer: 536

Question 10.

863 – 50 = _______

Answer: 813

Question 11.

238 – 70 = _____

Answer: 168

Question 12.

617 – 400 = _____

Answer: 217

**Round each number to the nearest ten.**

Question 13.

65 is about _________

Answer: 65 is rounded to the nearest ten is 70.

Question 14.

132 is about ____.

Answer: 132 is rounded to the nearest ten is 130.

Question 15.

29 is about ____.

Answer: 29 is rounded to the nearest ten is 30.

Question 16.

396 is about ____.

Answer: 396 is rounded to the nearest ten is 400.

**Find the sum or difference. Then round each number to the nearest ten to check that the answers are reasonable.**

Question 17.

76 + 83 = _______

___ + ____ = ____

Answer: 159

80 + 80 = 160

Explanation:

We need to round the numbers to the nearest ten

76 is nearer to 80,

83 is nearer to 80,

By adding 76 with 83 we get 159,

By adding 80 with 80 we get 160,

Therefore, the estimated sum is 160.

Question 18.

182 + 95 = _______

____ + ____ = ____

Answer:

182 + 95 = 277

180 + 100 = 280

Explanation:

We need to round the numbers to the nearest ten

182 is nearer to 180,

95 is nearer to 100,

By adding 182 to 95 we get 277

By adding 180 to 100 we get 280,

Therefore, estimated sum is 280

Question 19.

628 – 145 = _________

____ + ___ = ____

Answer:

628 – 145 = 483

Explanation:

We need to round the numbers to the nearest ten

628 is nearer to 630,

145 is nearer to 150,

By subtracting 145 from 628 we get 483,

By subtracting 150 from 630 we get 480,

Therefore, the estimated sum is 480.

Question 20.

598 – 136 = _________

____ – ____ = ____

Answer: 598 – 136 = 462

Explanation:

598 is nearer to 600,

136 is nearer to 140,

By subtracting 136 from 598 we get 462,

By subtracting 140 from 600 we get 460,

Therefore estimated sum is 460

**Problem Solving**

**Solve. Then use estimation to check that the answers are reasonable.**

Question 21.

Mrs. Brown buys a set of books and a giant teddy bear. The set of books costs $154. The giant teddy bear costs $122. Find the sum of the amount for both prices.

___ + ___ = ____

Check: ___ + ___ = ____

Is the answer reasonable? Explain

The two things cost about $ _______

Answer:

The sum of the amount for both prices is $ 276

154 + 122 = 276

Explanation:

Given,

Mrs. Brown buys a set of books cost of = $154,

Buys a giant teddy bear cost of = $122,

By adding both $154 to $122 we get the total sum of $276,

Therefore, the total amount for both prices is $276.

Question 22.

Pete earns $103 a month delivering newspapers. Shawn earns $175 a month delivering pizzas. What is the difference in the amounts they earn?

_____ – ____ = ____

Check: ___ – ____ = ____

Is the answer reasonable? Explain.

The difference is about $ ____

Answer:

The difference in the amounts they earn is $72.

Explanation:

Given,

Pete earns monthly by delivering newspapers is = $103

Shawn earns monthly by delivering pizzas is = $175

By subtracting 103 from 175 we get 72,

Therefore, we get the difference in amounts they earn is $72.