Question

find the sum of - 1/3 - 4/5

Answer 1

hope this helps
1/(2*3) can be written as 1/2 - 1/3.
1/(3*4) can be written as 1/3 - 1/4.

And so on until
1/(49*50) can be written as 1/49 - 1/50.

When you add up this series, you get 1/2 - 1/50, which is 24/50 which is 12/25.