Chapter 6Multiply and Divide Decimals

Lesson 1 – Estimate Products of Whole Numbers and Decimals

Round to the ones place.

Example: Estimate 15.8 x 5

15.8 → 16 x 5 → x 5

80

Lesson 3 – Multiply Decimals by Whole Numbers

When multiplying a decimal by a whole number, place the decimal point in your answer directly below where it is in the problem.

Examples –

1.) 2 × 0.53 0.53 2.) 12 × 0.712

× 2 × 0.7

1.06 8.4

Lesson 5 – Multiply Decimals

When multiplying a decimal by a decimal, move the decimal points all the way to the right to make it a whole number. In your answer, move the decimal point the same number of places to the left.

0.52 52 2 decimal places x 0.6 x 6 + 1 decimal

place 312. 3 decimal places

312. = 0.312 – move decimal point 3 places to the left.

*If there are no more numbers on the left, you must add zeros.

Lesson 8 – Multiplication Properties

Commutative Property of Multiplication The order in which the factors are multiplied does not

change the product. Ex. – 5 x 4 = 4 x 5

Associative Property of Multiplication The way in which the numbers are grouped does not

change the product. Ex. – (7 x 3) x 9 = 7 x (3 x 9)

Identity Property of Multiplication The product of any number and 1 equals the number. Ex. - 12 x 1 = 12

Lesson 9 – Estimate Quotients

Use compatible numbers to divide. Remember, the numbers must go in evenly – no remainders!

Example: $17.50 ÷ 7 → $ 18 ÷ 7

*Does not go in evenly – pick different numbers

$21 ÷ 7 = $3 or 14 ÷ 7 = 2

Lesson 11 – Divide Decimals by Whole Numbers You DO NOT need to use models. The steps are simple.

Write the decimal point in your answer DIRECTLY ABOVE where it is in the problem.

↓ __.__

3) 4.2

Divide as you would divide a whole number. _1.4__

3) 4.2 -3 ↓ 12 -12

0

Lesson 13 – Divide Decimals

1. Move the decimal point in the divisor to make it a whole number.

2. Move the decimal point in the dividend the same number of places.

3. Place the decimal point and divide.

_____ ______ o.05) 4.205 → o05.) 420.5

↑ 2 places ↑ _ 84.1 to the right5) 420.5 -40↓ 20

-20↓ 05

- 05 0