1. Multiplying
Decimals

2. 3.15 x 1.9
Round to the nearest whole number to estimate answer
3 x 2
= 6
So our answer should be somewhere around 6
Do the multiplication (just ignore the decimals for now) 1 4
315
x 19 28 3 5 3 1 5 5 9 8 5

3. 6 5 9 8 5 . Our estimate Answer before doing anything with decimals
Based on our estimate, where do you think the decimal should go?
Let’s look at another example to see if we can come up with a rule…..

4. 2.7 x 1.1
Round to the nearest whole number to estimate answer
3 x 1
= 3
So our answer should be somewhere around 3
Do the multiplication (just ignore the decimals for now) 27
x 11 2 7 2 7 2 9 7

5. Based on our estimate, where do you think the decimal should go?3
Answer before doing anything with decimals
2 9 7 .
Based on our estimate, where do you think the decimal should go?
One more example…..

6. 4.125 x 1.8
Round to the nearest whole number to estimate answer
4 x 2
= 8
So our answer should be somewhere around 8
Do the multiplication (just ignore the decimals for now) 1 2 4
4125
x 18 33 4 1 2 5 7 4 2 5

7. 8 7 4 2 5 0 . Our estimate Answer before doing anything with decimals
Based on our estimate, where do you think the decimal should go?
Ok, lets look at all of our examples…..

8. Number of Decimal Places in problem
Number of Decimal Places in answer
Problem
Answer
3.15 x 1.9 3
5.985 3
2.7 x 1.1 2
2.97 2
4.125 x 1.8 4
7.4250 4
Look at the number of places after the decimal point in both the problem and the answer……

9. How to multiply decimals1 2 3
Estimate
the
products
first.
Multiply
(ignore
decimal)
Count the # of digits
in decimal places in
the factors. That’s the
number of decimal
places in the product.
123
4.235
1.8 x x
4.235 6 1. x
4.235 6
7 6230 1. 4 4 2 .
76230 8
1234
Copyright © 2013 by Monica Yuskaitis

10. Solve this problem 3 2
9. 8 7 x
. 4
3 9 . 4 8

11. Solve this problem
5. 2 3
. 2 1 x 5 2 3 +
1 0 4 6 x 1 . 9 8 3

12. 7 6. 8 x 4. 3 5 3 8 4 2 3 4 x 3 0 7 2 x x 3 3 4 . 8 Solve this problem1
3 8 4 1
2 3 4 x
3 0 7 2
x x + 3 3 4 . 8

13. Problem
Solving

14. George lived 13. 7 miles from his school. He walked 1/2 (
George lived 13.7 miles from his school. He walked 1/2 (.5) of the way. How far did he walk?
13.7 miles

15. .5 of 13.7
The first thing to remember is “of” means multiply in mathematics. of x =

16. .5 x 13.7 1 3
1 3.7 . 5 x 6 . 8 5
miles