MULTIPLYING DECIMALS

NS 1.4 Calculate given percentages of quantities and solve problems involving discounts at sales, interests earned, and tips. Today’s objective: learn how to multiply decimals together, paying special attention to where the decimal point goes in the answer

Solve these problems: Pretend the decimal point isn’t there. 4×9 4.0 × × = 4.0 = 4.00 and 9 = 9.0 so the answers should all be equal. Place a decimal point the answers to make them all equal. × = 36 = 360 = = 36 = 36.0 = = 36.0 =

How do we multiply decimals? First, ignore the decimal points and multiply like normal. Count how many digits are to the right of the decimal points in both of the numbers you multiplied together. Place a decimal point in your answer so that it has the same number of digits to the right of it.

3.2 × × There are two digits to the right of the decimal points. Place a decimal point in the answer two digits from the right. 3.2 ×

How do we multiply a decimal by an integer? 31.2 × 4 Do not count any digits to the right of a decimal point for integers × There is only one digit to the right of the decimal point, so put the decimal point one digit from the right of the answer.

1.03 × × × × = 73.1

Direct Station We will work together on word problems that involve decimal multiplication.

Collaborative Station You and your partner will each be doing a decimal multiplication problem. Even though each partner will have slightly different numbers, they are very close. For example, Partner A has 6.3 × 4.1 and Partner B has 6.32 × 4.1 Therefore, both Partners should get very similar answers! If one Partner’s answer is much bigger or smaller than the other Partner’s, that most likely means someone put the decimal point in the wrong place of their answer!

Independent Station We are switching to ST Math’s unit on multiplying decimals. Write down the work for all multiplication problems you do.