The usual price of a pen sold at Shop L and M is $35. During a sale, a discount of 20% is given to every pen sold at Shop L. At Shop M, a discount of 60% is given to the 7th pen for every 7 pens sold. How much cheaper would it be if Erika buys 16 pens from Shop L instead of Shop M?

	Shop L	Shop M
Price of 1 pen	80%  $28	100% $35
Every 7th pen		40% $14

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

Price of 1 pen from Shop L at 20% discount
= 80% x 35
= ⁸⁰₁₀₀ x 35 
= $28

Cost of 16 pens from Shop L
= 16 x 28
= $448

Price of the 7th pen from Shop M in percentage
= 100% - 60%
= 40%

Cost of 7th pen at Shop M
= 40% x 35
= ⁴⁰₁₀₀ x 35 
= $14

Cost of 1 set of 7 pens at Shop M
= 35 x 6 + 14
= $224

Number of sets of 7 for pens at Shop M
= 16 ÷ 7
= 2 r 2

Cost of 2 sets of 7 pens at Shop M
= 2 x 224
= $448

Cost of 2 pens at Shop M
= 2 x 14
= $28

Cost of 16 pens at Shop M
= 448 + 28
= $476

Amount cheaper if Erika buys 16 pens from Shop L instead of Shop M
= 476 - 448
= $28

Answer(s): $28