The usual price of a notebook sold at Shop K and L is $20. During a sale, a discount of 20% is given to every notebook sold at Shop K. At Shop L, a discount of 60% is given to the 7th notebook for every 7 notebooks sold. How much cheaper would it be if Risa buys 16 notebooks from Shop K instead of Shop L?

	Shop K	Shop L
Price of 1 notebook	80%  $16	100% $20
Every 7th notebook		40% $8

Price of 1 notebook from Shop K in percentage
= 100% - 20%
= 80%

Price of 1 notebook from Shop K at 20% discount
= 80% x 20
= ⁸⁰₁₀₀ x 20 
= $16

Cost of 16 notebooks from Shop K
= 16 x 16
= $256

Price of the 7th notebook from Shop L in percentage
= 100% - 60%
= 40%

Cost of 7th notebook at Shop L
= 40% x 20
= ⁴⁰₁₀₀ x 20 
= $8

Cost of 1 set of 7 notebooks at Shop L
= 20 x 6 + 8
= $128

Number of sets of 7 for notebooks at Shop L
= 16 ÷ 7
= 2 r 2

Cost of 2 sets of 7 notebooks at Shop L
= 2 x 128
= $256

Cost of 2 notebooks at Shop L
= 2 x 8
= $16

Cost of 16 notebooks at Shop L
= 256 + 16
= $272

Amount cheaper if Risa buys 16 notebooks from Shop K instead of Shop L
= 272 - 256
= $16

Answer(s): $16