In July, Pierre gave his wife, Zoe, $4000 for household expenditure. Zoe spent 70% of the sum on rental, 10% on food and saved the rest. In August, Pierre reduced the sum he gave to Zoe. Zoe 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 August. By what percentage was the sum given to Zoe reduced by?

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

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

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

Total amount that Pierre 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 Pierre spent on rental and food is repeated. 

80 u = 78% 

80 u = 3120

1 u = 3120 ÷ 80 = 39

Amount that Pierre gave to Zoe in August
= 100 u
= 100 x 39
= $3900

Amount that Zoe received less from Pierre from July to August
= 4000 - 3900
= $100

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

Answer(s): 2.5%