What fraction is bigger 8/15 or 14/25?

The first thing to do is to make the denominators the same: 
  8/15 = 40/75
14/25 = 42/75

42/75 is bigger than 40/75.  Therefore, 14/25 is bigger than 8/15. 

In order to solve these problems, you would have to change the fractions so that they have equal denominators. In order to do so, you must find the LCM of the denominators, in this case 15 and 25.

The LCM is 75 for these two numbers. Now, you change the fractions based on their new denominators.

8/15 = 40/75
14/25 = 42/75

I got this by dividing 75 by the previous denominators and multiplying that result by the original numerators. (i.e. 75/25 = 3 * 14 = 42)

So, now that you've changed both fractions to have equal denominators, you can see, by the numerators, which of the two is bigger.

Your answer is 14/25.

Hope this is clear and helps you out for future problems :)