Question

A CD which usually sells for $15.78 has a 15% discount. Estimate the amount of the discount.

Answer 1

if we take 15.78 to be the 100%, what is the 15%?

$\bf \begin{array}{ccll} amount&\%\\ \text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\ 15.78&100\\ a&15 \end{array}\implies \cfrac{15.78}{a}=\cfrac{100}{15}\implies \cfrac{15.78\cdot 15}{100}=a$

Answer 2

You need to round 15.78 to get 16. You then multiply 16 to 15 and divide by 100 to get your answer :

2.4

Which would also be $2.40