Billy's and Tiffany's monthly allowances were the same at first. Billy's allowance increased by 20% while Tiffany's decreased by 10%. Given that Billy's allowance would decrease by another 25% if he had received $843 less from his fathers, find the difference in the children's monthly allowances.

	Billy	Tiffany
Before	1 u	1 u
Change 1	+ 0.2 u	- 0.1 u
After 1	1.2 u	0.9 u
Change 2	- 0.3 u	No change
After 2	0.9 u	0.9 u

Increase in Billy's allowance
= 20% x 1 u
= ²⁰₁₀₀ x 1 u
= 0.2 u

Decrease in Tiffany's allowance
= 10% x 1 u
= ¹⁰₁₀₀ x 1 u
= 0.1 u

Decrease in Billy's allowance if he had received $843 less from his fathers
= 25% x 1.2 u
= ²⁵₁₀₀ x 1.2 u
= 0.3 u

0.3 u = 843

1 u = 843 ÷ 0.3 = 2810

Difference in the allowance between Billy and Tiffany
= 1.2 u - 0.9 u
= 0.3 u
= 0.3 x 2810
= $843

Answer(s): $843