How to Multiply Decimals | BEST Math Review


Multiplying Decimals
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Multiplying Decimals


Multiplying decimals. When multiplying decimals; instead of lining up the decimal point we line up the last digits on the right. If we are multiplying 4.23 times 9.075 we want to line up our last digits.


Three is the last digit in 4.23 and 5 is the last digit in 9.075. Here’s my seven my zero my decimal and nine. Now, we multiply just like we multiply whole numbers.


Starting with 5; 5 times 3 is 15, carry the 1, 5 times 2 is 10, plus 1 is 11, carry the 1. 5 times 4 is 20, plus 1 is 21, and then I’ll get rid of these for our next number. Now that we’re multiplying times the 7, we need a zero placeholder.


7 times 7 is 21. Write your 1, carry your 2. 7 times 2 is 14, plus 2 is 16, write you 6 carry your 1. 7 times 4 is 28 plus 1 is 29. Get rid of those, then we need two zeros for placeholders. When we multiply times 0; 0 times 3 is 0, 0 times 2 is 0, 0 times 4 is 0.


We just get a line of zeros. Moving on to our last digit. Now, we need three 0 placeholders, before we multiply times nine; 9 times 3 is 27. Write 7 carry the 2. 9 times 2 is 18, plus 2 is 20. Write the 0 carry the 2. 9 times 4 is 36 plus 2 is 38 .


Then just like we would with any other whole numbers, we’re going to add our results together. 5 plus all these 0’s gives us 5.1 plus 1 is 2. 1 plus 6 is 7. 2 plus 9 is 11 plus 7 is 18. Write our 8 carrier our 1. 1 plus 2 is 3. Then we have 8 and our 3.


To determine where the decimal point goes when you’ve multiplied your decimals together; we’re going to take how places, how many numbers there were behind our decimal in our first number, and how many numbers there were behind our decimal in our second number and add those together.


Since we had two numbers behind the decimal here and three numbers behind the decimal here then our result will have five numbers behind the decimal. 2 plus 3 is 5. 1,2,3,4,5. This is the result of multiplying my two decimals together.



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Last updated: 10/22/2018

 

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