This fraction is giving me a hard time.?

You need to find the lowest common multiple of the denominators (18, 2, 4 and 16)

2 and 4 go into 16 evenly, so 2 and 4 won't influence the lcm
lcm(18, 2, 4, 16)
=lcm(18, 16)

Factorizing:
18 = 2 x 3 x 3
16 = 2 x 2 x 2 x 2

There is a common factor of 2
lcm(18,16)
= (18 x 16) / 2
= 18 x 8
= 144

You now need to scale up each fraction to the new denominator (144), and then you will be able to do the addition and subtraction of the scaled numerators.

(-15 x 8) + (5 x 72) - (-7 x 32) - (9 x 9)
------------------------------------------------------
144

... You do the arithmetic :)

Calculator to check your lowest common multiples here
http://statsfiddle.info/Primes/LowestCommonMultiple/18?number2=16...Show more

Find you common denominator first it is 288 To find this multiply your two largest numbers against each other which is 288. Now convert all fractions to a fraction of 288 and perform the functions.

-240/288 + 720/288 + 504/288 - 162/288 = 822/288 now reduce the fraction 411/144 and further reduce it: 2 and 123/144 there is another method but this is the easiest and fasted for me....Show more

= -15/18+5/2+7/4-9/16
= (-120+360+252-81)/144
= 441/144
= 49/16...Show more

Set a common denominator. It looks like it will be whatever is 18 x 16. Multiply all the fractions (top and bottom) so that the bottom equals the common denominator, and then add/subtract....Show more