The number of seats in an auditorium is increased by 25% and the price of a ticket is increased by 12%. By what percentage does the revenue increase?

Revenue increases by 40%.

Revenue = seats x ticket price.

Seats become 1.25 times, price becomes 1.12 times.

New revenue = 1.25 x 1.12 = 1.40 times the old.

Increase = 1.40 - 1 = 0.40 = 40%.

So revenue rises 40%.