All the solutions provided in **McGraw Hill Math Grade 3 Answer Key PDF Chapter 2 Lesson 7 Add Three-Digit Numbers** will give you a clear idea of the concepts.

## McGraw-Hill My Math Grade 3 Answer Key Chapter 2 Lesson 7 Add Three-Digit Numbers

When you add, you may need to regroup. To regroup means to rename a number using place value.

**Math in My World**

Example 1

During a weekend trip to Vermont, the Wildlife Club saw 127 wrens and 58 eagles. How many wrens and eagles did the Wildlife Club see?

Find 127 + 58.

Check for Reasonableness

185 is close to the estimate of 190. It makes sense. The answer is reasonable.

127 + 58 = 185

So, the Wildlife Club saw 185 wrens and eagles.

You can write a number sentence to find the unknown, or missing number.

Example 2

One box of butterfly nets costs SI75. Another box costs $225. How much do the boxes of nets cost altogether?

Write a number sentence to find the unknown.

2. Add the tens and hundreds.

1 ten + 7 tens + 2 tens = 10 tens

Regroup 10 tens as 1 hundred and 0 tens.

1 hundred + 1 hundred + 2 hundreds = 4 hundreds

Check for Accuracy

Use the Commutative Property to check your answer.

No matter in which order you add, the sum is the same.

So, $175 + $225 =$400. The unknown is $400. The net cost $400.

**Talk Math**

Why is it important to check for reasonableness?

Answer:

Checking for reasonableness is a process by which students evaluate estimations to see if they are reasonable guesses for a problem.

To be reasonable means to be as much as is appropriate or fair.

In math, reasonableness can be defined as checking to verify that the result of the solution or the calculation of the problem is correct or not, be either estimating or by plugging in your result to check it.

**Guided Practice**

**Add.**

Question 1.

Answer:

Explanation:

1. Add the ones

4 ones + 7 ones = 11 ones.

regroup 11 ones as 1 ten and 1 one

2. Add the tens and hundreds.

1 ten + 6 ten + 1 ten = 8 ten

1 hundred + 0 hundred = 1 hundred

So 164 + 17 = 181

Question 2.

Answer:

Explanation:

1. Add the ones

6 ones + 9 ones = 15 ones.

regroup 15 ones as 1 ten and 5 one

2. Add the tens and hundreds.

1 ten + 5 ten + 2 ten = 8 ten

1 hundred + 2 hundred = 3 hundred

So 156+ 229= 385

**Independent Practice**

**Add. Check for reasonableness.**

Question 3.

Estimate:

780

Answer:

Explanation:

1. Add the ones

9 ones + 9 ones = 18 ones.

regroup 18 ones as 1 ten and 8 one

2. Add the tens and hundreds.

1 ten + 5 ten + 1 ten = 7 ten

7 hundred + 0 hundred = 7 hundred

So 759+ 19= 778

778 is close to estimate of 780

Question 4.

Estimate:

470

Answer:

Explanation:

1. Add the ones

5 ones + 6 ones = 11 ones.

regroup 18 ones as 1 ten and 1 one

2. Add the tens and hundreds.

1 ten + 4 ten + 2 ten = 7 ten

4 hundred + 0 hundred = 4 hundred

So 445+ 26= 471

471 is close to estimate of 475

Question 5.

Estimate: 440

Answer:

Explanation:

1. Add the ones

5 ones + 3 ones = 8 ones.

2. Add the tens and hundreds.

4 ten + 9 ten = 13 ten

regroup 13 ten as 1 hundred and 3 ten

1 hundred + 3 hundred = 4 hundred

So $345+ $93= $438

438 is close to estimate of 440

Question 6.

Estimate:

640

Answer:

Explanation:

1. Add the ones

7 ones + 7 ones = 14 ones.

regroup 14 ones as 1 ten and 4 one

2. Add the tens and hundreds.

1 ten + 2 ten + 1 ten = 4 ten

4 hundred + 2 hundred = 6 hundred

So $427+ $217= $644

644 is close to estimate of 650

Question 7.

Estimate:

650

Answer:

Explanation:

1. Add the ones

7 ones + 1 ones = 8 ones.

2. Add the tens and hundreds.

9 ten + 5 ten = 14 ten

regroup 14 tens as 1 hundred and 4 ten

1 hundred + 5 hundred = 6 hundred

So 597+ 51= 648

648 is close to estimate of 651

Question 8.

Estimate:

300

Answer:

Explanation:

1. Add the ones

9 ones + 9 ones = 18 ones.

regroup 18 ones as 1 ten and 8 ones

2. Add the tens and hundreds.

7 ten + 1 ten + 1 ten = 9 ten

2 hundred + 0 hundred = 2 hundred

So 279+ 19= 298

298 is close to estimate of 300

**Add. Use the Commutative Property of Addition to check for accuracy.**

Question 9.

Answer:

Explanation:

No matter in which order you add, the sum is the same.

Question 10.

Answer:

Explanation:

No matter in which order you add, the sum is the same.

**Algebra Add to find the unknown.**

Question 11.

The unknown is ____.

Answer:

Explanation:

1. Add the ones

3 ones + 7 ones = 10 ones.

regroup 10 ones as 1 ten and 0 one

2. Add the tens and hundreds.

1 ten + 4 ten + 1 ten = 6 ten

2 hundred + 0 hundred = 2 hundred

So 43+ 217= 260

The unknown is 260

Question 12.

The unknown is ____.

Answer:

Explanation:

1. Add the ones

7 ones + 7 ones = 14 ones.

regroup 14 ones as 1 ten and 4 one

2. Add the tens and hundreds.

1 ten + 0 ten + 2 ten = 3 ten

6 hundred + 0 hundred = 6 hundred

So 607+ 27= 634

The unknown is 634

Question 13.

The unknown is ____.

Answer:

Explanation:

1. Add the ones

3 ones + 1 ones = 4 ones.

2. Add the tens and hundreds.

7 ten + 9 ten = 16 ten

regroup 16 tens as 1 hundred and 6 ten

1 hundred + 1 hundred + 5 hundred= 7 hundred

So 173+ 591= 764

The unknown is 764

**Problem Solving**

**Write a number sentence with a symbol for the unknown. Then solve.**

Question 14.

A 10-speed bike is on sale for Si 99, and a 12-speed racing bike is on sale for $458. How much do the two bikes cost altogether?

Answer:

two bikes cost altogether 557

Explanation:

10-speed bike is on sale for Si 99

12-speed racing bike is on sale for $458

Si 99 + $ 458 = 557

Question 15.

**Mathematical PRACTICE 2 Use Algebra** A newspaper surveyed 475 students about their favorite sport. A magazine surveyed 189 students about their favorite snack. How many students were surveyed by the magazine and newspaper?

Answer:

students surveyed by the magazine and newspaper are 664

Explanation:

newspaper surveyed 475 students

A magazine surveyed 189 students

Total 475 + 189 = 664

**HOT Problems**

Question 16.

**Mathematical PRACTICE 2 Use Number Sense** Use the digits 3, 5, and 7 to make two three-digit numbers with the greatest possible sum. Use each digit one time in each number. Write a number sentence.

Answer:

The two three digit numbers are 735 and 537

735 + 537 = 1272

Question 17.

**Building on the Essential Question** How can I use place value to add three-digit numbers?

Answer:

For example add 123 + 123 = 246

Explanation:

1. Add the ones

3 ones + 3 ones = 6 ones.

2. Add the tens and hundreds.

2 ten + 2 ten = 4 ten

1 hundred + 1 hundred = 2 hundred

So 123+ 123= 246

### McGraw Hill My Math Grade 3 Chapter 2 Lesson 7 My Homework Answer Key

**Practice**

**Add. Check for reasonableness.**

Question 1.

Estimate:

280

Answer:

Explanation:

1. Add the ones

8 ones + 9 ones = 17 ones.

regroup 17 ones as 1 ten and 7 one

2. Add the tens and hundreds.

1 ten + 7 ten + 9 ten = 17 ten

regroup 17 tens as 1 hundred and 7 ten

1 hundred + 1 hundred = 2 hundred

So 178+ 99= 277

Question 2.

Estimate:

Answer:

Explanation:

1. Add the ones

5 ones + 1 ones = 6 ones.

2. Add the tens and hundreds.

9 ten + 4 ten = 13 ten

regroup 13 tens as 1 hundred and 3 ten

1 hundred + 6 hundred + 1 hundred= 8 hundred

So 695+ 141= 836

Estimate: 840

Question 3.

Estimate:

Answer:

Explanation:

1. Add the ones

7 ones + 6 ones = 13 ones.

regroup 13 ones as 1 ten and 3 ones

2. Add the tens and hundreds.

1 ten + 2 ten + 5 ten= 8 ten

3 hundred + 0 hundred = 3 hundred

So 327+ 56= 383

Estimate: 380

**Add. Use the Commutative Property to check for accuracy.**

Question 4.

Answer:

Explanation:

No matter in which order you add, the sum is the same.

Question 5.

Answer:

Explanation:

No matter in which order you add, the sum is the same.

**Algebra Add to find the unknown.**

Question 6.

The unknown is

Answer:

The unknown is 661 + 99 = 760

Question 7.

The unknown is

Answer:

The unknown is 258+ 337= 595

Question 8.

The unknown is

Answer:

The unknown is 739+ 81= 820

**Problem Solving**

Question 9.

**Mathematical PRACTICE 1 Make a Plan** The principal ordered 215 muffins and 155 bagels. How many muffins and bagels were ordered in all?

Answer:

In total 370

Explanation:

The principal ordered 215 muffins and 155 bagels

so 215 + 155 = 370

**Vocabulary Check**

**Choose the correct word to complete each sentence.**

reasonable regroup unknown

Question 10.

To ____ means to rename a number using place value.

Answer:

regroup

Explanation:

regroup means to rename a number using place value.

Question 11.

A missing number is the _____

Answer:

unknown

Explanation:

A missing number is the unknown

Question 12.

If an answer makes sense, it is _____

Answer:

reasonable

Explanation:

If an answer makes sense, it is reasonable

**Test Practice**

Question 13.

Mrs. Lewis bought two statues for her garden. One cost $145 and one cost $262. What was the total cost?

A. $117

B. $317

C. $407

D. $410

Answer:

C

Explanation:

$145 + $262 = $407

the total cost is $407