At a sale, shirts were sold for $15 each. This price was 20% off their original price. What
was the original price?

$ 18.75

Step-by-step explanation: Do not be tempted to increase $15 by 20% thinking that will make the original 100%. 20% of the original amount and 20% of the reduced amount are different quantities.

There are several different approaches:

Method 1: direct proportion

Compare the values with their corresponding percentages.

15

80

=

x

100

⇒

x

=

15

×

100

80

:

x

=

$

18.75

Method 2: form an equation and solve it

Let the original amount be

x

80

100

×

x

=

15

⇒

x

=

15

×

100

80

x

=

$

18.75

Method 3. Increase 15 in the ratio 100 : 80

15

×

100

80

x

=

$

18.75

Method 4: unitary method

$15 represents 80%

15

80

represents

1

%

15

80

×

100

represents

100

%

$

18.75

Notice that in each case, although the approach and reasoning were different, the calculations and the answer were the same.

The important thing is to recognise that this is a reverse percentage calculation, because the original amount is not known.

you bought 31 v bucks

step-by-step explanation:

25+6=31