The usual price of a pen sold at Shop S and T is $20. During a sale, a discount of 20% is given to every pen sold at Shop S. At Shop T, a discount of 50% is given to the 5th pen for every 5 pens sold. How much cheaper would it be if Shannon buys 12 pens from Shop S instead of Shop T?

	Shop S	Shop T
Price of 1 pen	80%  $16	100% $20
Every 5th pen		50% $10

Price of 1 pen from Shop S in percentage
= 100% - 20%
= 80%

Price of 1 pen from Shop S at 20% discount
= 80% x 20
= ⁸⁰₁₀₀ x 20 
= $16

Cost of 12 pens from Shop S
= 12 x 16
= $192

Price of the 5th pen from Shop T in percentage
= 100% - 50%
= 50%

Cost of 5th pen at Shop T
= 50% x 20
= ⁵⁰₁₀₀ x 20 
= $10

Cost of 1 set of 5 pens at Shop T
= 20 x 4 + 10
= $90

Number of sets of 5 for pens at Shop T
= 12 ÷ 5
= 2 r 2

Cost of 2 sets of 5 pens at Shop T
= 2 x 90
= $180

Cost of 2 pens at Shop T
= 2 x 10
= $20

Cost of 12 pens at Shop T
= 180 + 20
= $200

Amount cheaper if Shannon buys 12 pens from Shop S instead of Shop T
= 200 - 192
= $8

Answer(s): $8