In July, David gave his wife, Gillian, $3000 for household expenditure. Gillian spent 60% of the sum on rental, 30% on food and saved the rest. In August, David reduced the sum he gave to Gillian. Gillian spent the same amount on rental and reduced the amount she spent on food by 30%. She saved the remaining 10% of the sum given to her in August. By what percentage was the sum given to Gillian reduced by?

	Rental	Food	Savings	Total
Before	60%	30%	10%	$3000
Change		- 9%	- ?	- ?
After	60%	21%
Comparing the amounts spent in August	90 u		10 u	100 u

Amount that David saved in percent
= 100% - 60% - 30%
= 10%

Amount that David reduced on food in percent
= 30% x 30%
= ³⁰₁₀₀ x 30
= 9%

Total amount that David spent on rental and food in percent
= 60% + 21%
= 81%

100% → 3000

1% → 3000 ÷ 100 = 30

81% → 81 x  30 = 2430

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

90 u = 81% 

90 u = 2430

1 u = 2430 ÷ 90 = 27

Amount that David gave to Gillian in August
= 100 u
= 100 x 27
= $2700

Amount that Gillian received less from David from July to August
= 3000 - 2700
= $300

Percentage that the sum given to Gillian was reduced by from July to August
= ³⁰⁰₃₀₀₀ x 100%
= 10%

Answer(s): 10%