Multiplication of Decimals
Date: 01/02/2002 at 11:03:43 From: Emma Subject: Multiplication of Decimals Find the value of 36.5 x 3.504. I ignored the decimals and worked out the answer and discovered that when the numbers after the decimals are added together, the decimal point can then be placed that number of places from the right. For example, the total number of decimal places moved for the sum above is four, and I know the answer is 1278960 and when the decimal point is placed the answer will be 127.8960. But I don't know why or how it always works. Can you please help me? Many thanks.
Date: 01/04/2002 at 02:31:38 From: Doctor Ann Subject: Re: Multiplication of Decimals Dear Emma, Thank you for writing to Dr. Math. You have asked a good question. I hope this explanation helps: Let's re-write your problem: 36.5 x 3.504 = 365 x (.1) x 3504 x (.001) (Do you agree with this?) Now use the commutative law to rearrange to: = 365 x 3504 x (.1) x (.001) = 1278960 x (.0001) (Do you recognize this?) I hope that from this you can see why you can "ignore the decimals and work out the problem" and then adjust the decimal point for the final answer. If you have another question, please feel free to write to Dr. Math. - Doctor Ann, The Math Forum http://mathforum.org/dr.math/
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.