# 3.4 Self-Check

The more you practice, the more your skills improve. Below are some exercises that will help you continue to develop your ability and check to make sure you understand the concepts discussed in this unit. Be sure to write your work out in your math notebook so that you can refer to it later if necessary.

## Exercise 1: Adding it Up

(a)

### Answer

(a)

Estimate:; this is close to the answer you calculated.

(b)

### Answer

(b)

Estimate: ; this is close to the answer you calculated.

(c)

### Answer

(c)

Estimate: 35 + 300 + 30 = 365; this is close to the answer you calculated.

(d)

### Answer

(d)

Estimate: 1030 + 3 + 330 = 1363: this is close to the answer you calculated.

## Exercise 2: Subtracting

For each subtraction problem, calculate the difference on paper, then use an estimate to check if your answer is reasonable. Check your work by using addition.

### Answer

(a)

Estimate:; this is close to the answer you calculated.

Check using addition:

(b)

### Answer

(b)

Estimate: ; this is close to the answer you calculated.

Check using addition: .

(c)

### Answer

(c)

Estimate: ; this is close to the answer you calculated.

Check using addition: .

(d)

### Answer

(d)

Estimate: this is close to the answer you calculated.

Check using addition: .

## Exercise 3: Multiplying

Carry out these calculations and then use an estimate to check whether your answer is reasonable.

(a)

### Answer

(a)

Estimate:; this is close to the answer you calculated.

Carry out these calculations and then use an estimate to check whether your answer is reasonable.

(b)

### Answer

(b)

Estimate:; this is close to the answer you calculated.

Carry out these calculations and then use an estimate to check whether your answer is reasonable.

(c)

### Answer

(c)

Estimate:; this is close to the answer you calculated.

**Exercise 4: Dividing**

Carry out these calculations and then use an estimate to check whether your answer is reasonable.

(a)

### Answer

(a)

Thus, .

Estimate: ; this is close to our answer you calculated.

(b)

### Answer

(b)

Thus, .

Estimate:; this is close to the answer you calculated.

(c)

### Answer

(c)

Thus, .

Estimate:; this is close to the answer you calculated.

3.3.12 Multiplication and Division Puzzle