Math Is Fun Forum

jmoore

Member

Registered: 2008-01-09

Posts: 25

How to times decimals?

Hello it was a long time agao since I was at school, anyway my question is this how do I times numbers like these

0.05 x 5.60 = (the answer is 0.28) but I am not sure how they got it.

I have tried setting the number up correctly like so:

   5.60
x 0.05
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but all I get is 0.00 as the answer

Thanks

Joe

luca-deltodesco

Member

Registered: 2006-05-05

Posts: 1,470

Re: How to times decimals?

the general idea is to completely ignore the fact that the decimal point is there, and treat the multiplication as if there was no decimal points in the two numbers. Then after finding the result, you put the decimal point in so that the number of fractional parts in the answer is the sum of that of the two numbers.

so in your example to make it clearer because i drag at explaining things with words

5.60 * 0.05.   560*5 = 2800
5.60 has 2 fractional parts
0.05 has 2 fractional parts. so their product has (2+2=4) fractional parts.

so the answer is 0.2800 = 0.28

basicly, you are multiplying each number by some power of 10, and then dividing the product to get the answer.

so say you have a number

ab.cd and xy.z

100*ab.cd = abcd
10*xy.z = xyz

ab.cd*xy.z = (abcd*xyz)/(100*10)

Last edited by luca-deltodesco (2008-04-23 23:25:29)

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jmoore

Member

Registered: 2008-01-09

Posts: 25

Re: How to times decimals?

Thanks Luca, you are a life saver if you have any problems with your pc please let me know then I can return the favor

jmoore

Member

Registered: 2008-01-09

Posts: 25

Re: How to times decimals?

So with this one am I doing it correctly

7.54
2.01

same as

754
201

times that which gives me 2154

add the decimal place back which should be 0.2154

I checked it on a calculator but my answer was wrong and I am not sure where I went wrong.

luca-deltodesco

Member

Registered: 2006-05-05

Posts: 1,470

Re: How to times decimals?

ehm... 754*201 = 151554, not 2154
which then gives the answer 15.1554

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The Beginning Of All Things To End.
The End Of All Things To Come.