In August, Tom gave his wife, Tammy, $4000 for household expenditure. Tammy spent 70% of the sum on rental, 10% on food and saved the rest. In September, Tom reduced the sum he gave to Tammy. Tammy 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 Tammy 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 Tom saved in percent
= 100% - 70% - 10%
= 20%

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

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

80 u = 78% 

80 u = 3120

1 u = 3120 ÷ 80 = 39

Amount that Tom gave to Tammy in September
= 100 u
= 100 x 39
= $3900

Amount that Tammy received less from Tom from August to September
= 4000 - 3900
= $100

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

Answer(s): 2.5%