David's and Sarah's monthly allowances were the same at first. David's allowance increased by 50% while Sarah's decreased by 40%. Given that David's allowance would decrease by another 40% if he had received $1422 less from his parents, find the difference in the children's monthly allowances.

	David	Sarah
Before	1 u	1 u
Change 1	+ 0.5 u	- 0.4 u
After 1	1.5 u	0.6 u
Change 2	- 0.6 u	No change
After 2	0.9 u	0.6 u

Increase in David's allowance
= 50% x 1 u
= ⁵⁰₁₀₀ x 1 u
= 0.5 u

Decrease in Sarah's allowance
= 40% x 1 u
= ⁴⁰₁₀₀ x 1 u
= 0.4 u

Decrease in David's allowance if he had received $1422 less from his parents
= 40% x 1.5 u
= ⁴⁰₁₀₀ x 1.5 u
= 0.6 u

0.6 u = 1422

1 u = 1422 ÷ 0.6 = 2370

Difference in the allowance between David and Sarah
= 1.5 u - 0.6 u
= 0.9 u
= 0.9 x 2370
= $2133

Answer(s): $2133