Question

Aron spent 3/8 of her allowance on a book and 2/5 of the remaining on pen. The cost of his pen is 30. How much is the cost of the book?

Answer 1

Let the allowance aaron has be: x
Spent 3/8 of allowance(x) on a book = Cost of book = \(\frac{3x}{8}\)
Remaining allowance = x-\(\frac{3x}{8}\) = \(\frac{5x}{8}\)

Spent 2/5 of "Remaining allowance" on a pen

= \(\frac{2}{5}\) of remaining

= \(\frac{2}{5}\) * \(\frac{5x}{8}\) = \(\frac{2x}{8}\) = \(\frac{x}{4}\)

Thus the pen cost him: \(\frac{x}{4}\) = 30
So x = 120.

But we do not stop here.
We need to find price of the book.
What was the price of the book?

\(\frac{3x}{8}\) = \(\frac{3*120}{8}\) = 45

Understood the question? :)