Allowance and money

Question

if a girl with an allowance of $X spends $Y, the fractional part of her allowance that she did not spend is 

A)X-Y/X

B) X-Y

C) Y/X

D) none of these 

Answer 1

A. make up a real life problem such as 

Mary gets an allowance of $30, (x).

She spends $10, (y). 

She does NOT spend $20 (x-y). 

What fraction is that of the original?

20/30 or 2/3, which is (x-y)/x