30 students collected money for donation. The average contribution was Rs.50 . Later on, their teacher also contributed some money. Now the average contribution is Rs.57 . What is the contribution of teachers ?

267

Total donation : 30 × 50 = 1500

Total donation including teacher: 31 × 57 = 1767

Donation given by teacher = 1767 - 1500 = Rs. 267