Which is bigger, 11/15 or 19/25 ?

When you're comparing fractions, the best thing to do is to find a common multiple between the two, and you can do this by listing the multiplies.
15-15 30 45 60 75 90 
25- 25 50 75 100

In this case, 75 is the smallest, so you multiply the first fraction by 5 and the second by 3.
11*5=55. 15*5= 75= 55/75
19*3= 57. 25*3=75= 57/75

In the current form, 57/75 is larger, therefore, 19/25 is larger than 11/15
Hope this helps :)