1. 1 Multiplying Decimals by Decimals

2. 2 DecimalReview

3. 3 Decimals Represent Fractions 6. 8 3 6 1 TenthsHundredthsThousandths 6 8/10 3/100 6/1000 1/10,000 Notice that every decimal ends with “ths”. OnesTen thousandths

4. 4 Which decimal place value is missing? Ten Thousandths Ones TenthsHundredths 6. 8 36 2 Ten Thousandths Thousandths

5. 5 Which decimal place value is missing? Thousandths Ones TenthsHundredths 6. 8 36 2 Ten Thousandths Thousandths

6. 6 Which decimal place value is missing? Tenths Ones TenthsHundredths 6. 8 36 2 Ten Thousandths Thousandths

7. 7 Which decimal place value is missing? Hundredths Ones TenthsHundredths 6. 8 36 2 Ten Thousandths Thousandths

8. 8 How to MultiplyDecimals

9. 9 3.15 x 1.9 3.15 x 1.9 Round to the nearest whole number to estimate answer Round to the nearest whole number to estimate answer 3 x 2 3 x 2 = 6 = 6 Do the multiplication (just ignore the decimals for now) Do the multiplication (just ignore the decimals for now) 315 315 x 19 x 19 5 4 3 1 28 501 3 5 8 9 5 So our answer should be somewhere around 6 So our answer should be somewhere around 6

10. 10 Our estimate 5 9 8 5 5 9 8 5 Based on our estimate, where do you think the decimal should go? Based on our estimate, where do you think the decimal should go? Answer before doing anything with decimals Answer before doing anything with decimals 6. Let’s look at another example to see if we can come up with a rule….. Let’s look at another example to see if we can come up with a rule…..

11. 11 2.7 x 1.1 2.7 x 1.1 Round to the nearest whole number to estimate answer Round to the nearest whole number to estimate answer 3 x 1 3 x 1 = 3 = 3 Do the multiplication (just ignore the decimals for now) Do the multiplication (just ignore the decimals for now) 27 27 x 11 x 11 72 7 0 2 7 92 So our answer should be somewhere around 3 So our answer should be somewhere around 3

12. 12 Our estimate 2 9 7 Based on our estimate, where do you think the decimal should go? Based on our estimate, where do you think the decimal should go? Answer before doing anything with decimals Answer before doing anything with decimals 3. One more example….. One more example…..

13. 13 4.125 x 1.8 4.125 x 1.8 Round to the nearest whole number to estimate answer Round to the nearest whole number to estimate answer 4 x 2 4 x 2 = 8 = 8 Do the multiplication (just ignore the decimals for now) Do the multiplication (just ignore the decimals for now) 4125 4125 x 18 x 18 0 4 0 2 0 5 0 2 1 05 2 4 So our answer should be somewhere around 8 So our answer should be somewhere around 8 1 33 4 7

14. 14 Our estimate 7 4 2 5 0 Based on our estimate, where do you think the decimal should go? Based on our estimate, where do you think the decimal should go? Answer before doing anything with decimals Answer before doing anything with decimals 8. Ok, lets look at all of our examples….. Ok, lets look at all of our examples…..

15. 15 Problem 7.4250 Number of Decimal Places in problem Answer Answer 4.125 x 1.8 2.7 x 1.1 3.15 x 1.9 2.97 5.985 Number of Decimal Places in answer 33 2 4 2 4 Look at the number of places after the decimal point in both the problem and the answer……

16. Copyright © 2013 by Monica Yuskaitis 16 x 4.235 61. x 4.235 6 7 6230 1. 4.235 1.8 x How to multiply decimals Estimate the products first. Count the # of digits in decimal places in the factors. That’s the number of decimal places in the product. 123 Multiply (ignore decimal) 4 2 8 76230 123 4. 1234

17. 17 Solve this problem 9. 8 7. 4 x 8 2 4 3 3 9.

18. 18 Solve this problem 5. 2 3. 2 1 x 325 6x41 0 + 3890.1

19. 19 Solve this problem 7 6. 8 4. 3 5 x 0 4 4 3 3 8 4x 2 0 2 2 3 x 273 0 32 + 0 8 0 1 4 1 33.

20. 20 ProblemSolving

21. 21 George lived 13.7 miles from his school. He walked 1/2 (.5) of the way. How far did he walk? 13.7 miles

22. 22.5 of 13.7 The first thing to remember is “of” means multiply in mathematics. of = x

23. 23.5 x 13.7 1 3.7. x 5 3 8 1 6. 5 miles