How Do U Find The Common Denominator Of A Fraction?

The common Denominator is a number that both the denominators are factors of.

For example.

1/2 + 2/5

you cant add 1/2 and 2/5 unless you change the lower number to be the same.  Doing this, you would multiply top and bottom numbers of both fractions by the same number so that both denominators are the same.

Easiest way to do this would be to multiply both denominators together.  2 x 5 = 10.
One problem with this is you would have to reduce it when its complete (maybe)

so that means that you would have top multiply the top numbers with the number you multiplied with on the bottom to get the common denominator.

So to make 1/2 with a 10 in the lower number, you would multiply the top number by 5.
And with 2/5,  you would multiply the top number by 2.

So your final fraction would be

1/2+2/5 = 5/10 + 4/10 = 9/10

no need to reduce.

You can multiply the two numbers to find the lcm.
or you could write out all the multiples of the two numbers
and then find the numbers that are multiples for both the numbers and circle them.
then smallest numbers will be the lcm