A man spends 75% of his income. His income increases by 20% and his expenditure also increases by 10%. Find the percentage increase in his savings.

let the income = rs 100

expenditure = 75% of his income = 75% of 100 = rs 75

savings = 100 - 75 = 25  ($$savings = income - expenditure$$)

income increases by 20%  

new income = 100 + $$\frac{20}{100} \times$$ 100 = 100 +20 =  rs 120

new expenditure = 75 + $$\frac{10}{100} \times$$ 75 = 75 + 7.5 = rs 82.5

new savings = 120 - 82.5 = 37.5 

increase in savings = new savings - initial savings = 37.5 - 25 = rs 12.5

% increase in savings = $$\frac{increase in savings}{initial savings} \times$$ 100 = $$\frac{12.5}{25} \times$$100 = 50%