Zoe spent 60% of her money on a number of marbles. She spent 25% of the remaining money on a few stamps and 40% of what was left on a number of pens.

1. What fraction of her money was left?
2. Given that the marbles cost $42 more than the pens, find the sum of money Zoe had at first.

(a)
60% = ⁶⁰₁₀₀ = ³₅

Fraction of money left after buying the marbles = 1 - ³₅ = ²₅

25% = ²⁵₁₀₀ = ¹₄

Fraction of remaining money after buying the stamps = 1 - ¹₄ = ³₄ 

40% = ⁴⁰₁₀₀ = ²₅

Fraction of what is left after buying the pens = 1 - ²₅ = ³₅

Fraction of money left after buying the marbles
= ²₅ x ³₄ x ³₅
= ⁹₅₀

(b)
Fraction of money spent on the pens
= ²₅ x ³₄ x ³₅
= ⁹₅₀

Fraction of money spent on the marbles
= ³₅
= ³⁰₅₀

Amount spent more on the marbles than the pens
= 30 u - 9 u
= 21 u

21 u = 42

1 u = 42 ÷ 21 = 2

Amount that Zoe had at first
= 50 u
= 50 x 2
= $100

Answer(s): (a) ⁹₅₀; (b) $100