deepak sir teaching

In a students queue, Kamal is 12th from left and Deepak is 18th from right. When Kamal and Deepak interchange their position, then Kamal is 25th from left. Find the total number of students in the queue.

Deepak said to Nitin, " That boy playing with the football is the younger of the two brothers of the daughter of my father's wife". How is the boy playing football related to Deepak ?

In a school there are 30 teachers who teach Mathematics or Physics. Of these teachers, 20 teach. Mathematics and 15 teach Physics, 5 teach both Mathematics and Physics. The number of teaches teaching only Mathematics is: