The numerator (top number of the fraction) is adding up by odd numbers in order.
From 1/40 to 4/40 you add 3, from 4/40 to 9/40 you add 5, from 9/40 to 16/40 you add 7, and from 16/40 to 25/40 you add 9.
The next number to add would logically be 11. So from 25/40 you would go to 36/40.
36/40 is your next fraction.
