Question : What is Suman's rank from the top in a class of forty students ?

Statements :
I. Suman is 3 ranks below Deepak from the top.
II. Deepak's rank from the bottom is 23.
III. Suman is 3 ranks above Deepak from the bottom.

From II, we conclude that in a class of 40, Deepak ranks 23rd from the bottom i.e. 18th from the top.
From I and II, we find that Suman is 3 ranks below 18th rank from the top i.e. she ranks 21st from the top.
From II and III, we find that Suman is 3 ranks above 23rd rank from the bottom
i.e. she ranks 20th from the bottom or 21st from the top.