hi can somebody tell me what the formula is to work out a unlike fraction for exp 17/20 - 3/5 = 1/4

Question

anonymous · Answer

take lcd of 20 and 5 = 20
(17(1) - 3(4))/20 =1/4

anonymous · Answer

thank you but could you make that a little easier because it was a little confusing sorry (:

anonymous · Answer

take lcd of 20 and 5 = the first number which 5 and 20 both have = 20
{17(number at which lcd is available at 20) - 3(number at which lcd is available at 5)}/20 
{17(1) - 3(4)}/20

anonymous · Answer

You got it? @finmath

anonymous · Answer

yes thanks you @sangya21

anonymous · Answer

anytime :)

anonymous · Answer

There is one more 9/10 -1/15 = something something =

anonymous · Answer

check lcd of 10 and 15 = 30 (both have 30 in their sequence) 
9(3)-1(2)/30 = 18-2/30