A boy spends ₹ 10 on first day, ₹ 20 on second day, ₹ 40 on third day and so on. Find how much in all, will he spend in 12 days?

G.P. formed = 10 + 20 + 40 + ........ Common ratio (r) = = 2. Hence, ₹10(2 12 - 1).