A man spends 75% of his income. His income increases by 20% and his expenditure increases by 10%. By what percentage do his savings increase?

Savings increase by 50%.

Take income 100; he spends 75, so saves 25.

New income = 100 x 1.2 = 120.

New expenditure = 75 x 1.1 = 82.5.

New savings = 120 - 82.5 = 37.5, rise = 37.5 - 25 = 12.5.

12.5 / 25 x 100 = 50%.