Question

A CD usually sells for $15.00. If the CD is 10% off, and sales tax is 5%, what is the total price of the CD, including tax?

Answer 1

The total price of the CD is $14.18

Explanation:

Percentages

We can compute additive or subtractive percentages by using these formulas. If we have a number X and want to increase it by Y%, then the increase is xY/100. Thus the new value for the number is x+xY/100 or equivalently

`X(1+Y/100)`

If we want to decrease by Z%, the new value is

`X(1-Z/100)`

The regular price for a CD is X=$15. The CD is Z=10% off, so the sale price is

`15(1-10/100)=\$13.5`

But we have to add the tax of Y=5%, so the final value is

`13.5(1+5/100)=\$14.18`

The total price of the CD is $14.18