Multiply Decimals by Whole Numbers Lesson 3 3

Multiply Decimals by Whole Numbers Lesson 3 -3

Objectives �I �I can multiply a decimal by a whole number. can solve a 2 -step story problem involving decimal numbers.

Example 1 Find 4 x 0. 83. 1) Count the number of digits to the right of the decimal. � 0. 83 – 2 digits 2) Multiply 4 x 83. � 83 X 4 332 3) Add the decimal back in with 2 places to the right. � 3. 32 4) Is my answer reasonable? 4 x 1=4, so yes.

Example 2 Find 3 x 14. 2. How many numbers to the right of the decimal? � 1 Multiply: � 142 x 3 426 Add the decimal back in with 1 digit to the right. � 42. 6 Is my answer reasonable? 3 x 14=42, so yes.

Got It? 1) 5 x 0. 25 2) 8 x 4. 47

Example 4 Find 2 x 0. 018. How many digits to the right of the decimal? � 3 Multiply: � 18 x 2 36 Add the decimal back in with 3 places to the right of the decimal. You need to annex a zero. � 0. 036

Example 5 Find 4 x 0. 012. Count the numbers to the right of the decimal. � 3 Multiply: � 12 X 4 48 Add the decimal back. Annex a zero. � 0. 048

Got It? 3) 3 x 0. 02 4) 0. 12 x 8

Example 6 A batch of trail mix calls for 1. 2 pounds of dry cereal. Logan is making 5 batches of trail mix. He already has 2. 2 pounds of cereal. How many more pounds of dry cereal does he need? Step 1: Multiply 1. 2 x 5 = 6 Step 2: Subtract 6 – 2. 2 = 3. 8 pounds

Got It? 5) Alexis buys 12 pencils for $0. 56 each. She pays with a $10 bill. How much change will she receive?

Homework Hints: #11. The answer is not 0. 2 mm. It’s saying that ONE quarter is 1. 75 mm and ONE nickel is 1. 95 mm. #14. Let’s take 12 x 3…it equals 36. 12 x 0. 3 is 3. 6. What is the difference?