In August, Ian gave his wife, Irene, $4000 for household expenditure. Irene spent 70% of the sum on rental, 10% on food and saved the rest. In September, Ian reduced the sum he gave to Irene. Irene spent the same amount on rental and reduced the amount she spent on food by 20%. She saved the remaining 20% of the sum given to her in September. By what percentage was the sum given to Irene reduced by?

	Rental	Food	Savings	Total
Before	70%	10%	20%	$4000
Change		- 2%	- ?	- ?
After	70%	8%
Comparing the amounts spent in September	80 u		20 u	100 u

Amount that Ian saved in percent
= 100% - 70% - 10%
= 20%

Amount that Ian reduced on food in percent
= 20% x 10%
= ²⁰₁₀₀ x 10
= 2%

Total amount that Ian spent on rental and food in percent
= 70% + 8%
= 78%

100% → 4000

1% → 4000 ÷ 100 = 40

78% → 78 x  40 = 3120

The total amount that Ian spent on rental and food is repeated. 

80 u = 78% 

80 u = 3120

1 u = 3120 ÷ 80 = 39

Amount that Ian gave to Irene in September
= 100 u
= 100 x 39
= $3900

Amount that Irene received less from Ian from August to September
= 4000 - 3900
= $100

Percentage that the sum given to Irene was reduced by from August to September
= ¹⁰⁰₄₀₀₀ x 100%
= 2.5%

Answer(s): 2.5%