11/15 + -2/5 what is the answer in fraction form

1/3 would be your answer 
you have to find the LCD than combine

Since we're adding fractions we'll need to make the denominator the same

5 fits into 15 three times

so we'll need to multiply both the numerator and denominator of -2/5 by 3

-2/5 becomes -6/15

now we can solve

11/15 + -6/15 = 5/15

5/15 can be written as 1/3 in simplified form