Question

Lucy bought a microwave oven at 10% off the original price. If she paid $21, what was the original price of the microwave?

Answer 1

The original price was $23.33

Explanation:

We can write this formula to solve this problem as:

`x - (10%` of `x) = $21`

"Percent" or "%" means "out of 100" or "per 100", Therefore 10% can be written as `10/100`.

When dealing with percents the word "of" means "times" or "to multiply".

So we can rewrite this equation as:

`x - (10/100 xx x) = $21`

`x - 10/100x = $21`

`(100/100 xx x) - 10/100x = $21`

`100/100x - 10/100x = $21`

`(100 - 10)/100x = $21`

`90/100x = $21`

`color(red)(100)/color(blue)(90) xx 90/100x = color(red)(100)/color(blue)(90) xx $21`

`cancel(color(red)(100))/cancel(color(blue)(90)) xx color(blue)(cancel(color(black)(90)))/color(red)(cancel(color(black)(100)))x = color(red)($2100)/color(blue)(90)`

`x = $23.33`