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

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 _____.

Question 3.
Add to find the ____________ of two or more numbers.

Question 4.
Subtract to find the ____________ between two or more numbers.

Question 5.
325 + 9 = _______

Question 6.
436 + 20 = _______

Question 7.
691 + 70 = _______

Question 8.
635 + 300 = _______

Subtract mentally.

Question 9.
541 – 5 = _______

Question 10.
863 – 50 = _______

Question 11.
238 – 70 = _____

Question 12.
617 – 400 = _____

Round each number to the nearest ten.

Question 13.
Answer: 65 is rounded to the nearest ten is 70.

Question 14.
Answer: 132 is rounded to the nearest ten is 130.

Question 15.
Answer: 29 is rounded to the nearest ten is 30.

Question 16.
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 = _______
___ + ____ = ____
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 = _______
____ + ____ = ____
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 = _________
____ + ___ = ____
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: ___ + ___ = ____
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: ___ – ____ = ____
The difference is about $____ Answer: The difference in the amounts they earn is$72.
Pete earns monthly by delivering newspapers is = $103 Shawn earns monthly by delivering pizzas is =$175