The usual price of a pen sold at Shop J and K is $40. During a sale, a discount of 25% is given to every pen sold at Shop J. At Shop K, a discount of 50% is given to the 4th pen for every 4 pens sold. How much cheaper would it be if Lynn buys 15 pens from Shop J instead of Shop K?

	Shop J	Shop K
Price of 1 pen	75%  $30	100% $40
Every 4th pen		50% $20

Price of 1 pen from Shop J in percentage
= 100% - 25%
= 75%

Price of 1 pen from Shop J at 25% discount
= 75% x 40
= ⁷⁵₁₀₀ x 40 
= $30

Cost of 15 pens from Shop J
= 15 x 30
= $450

Price of the 4th pen from Shop K in percentage
= 100% - 50%
= 50%

Cost of 4th pen at Shop K
= 50% x 40
= ⁵⁰₁₀₀ x 40 
= $20

Cost of 1 set of 4 pens at Shop K
= 40 x 3 + 20
= $140

Number of sets of 4 for pens at Shop K
= 15 ÷ 4
= 3 r 3

Cost of 3 sets of 4 pens at Shop K
= 3 x 140
= $420

Cost of 3 pens at Shop K
= 3 x 20
= $60

Cost of 15 pens at Shop K
= 420 + 60
= $480

Amount cheaper if Lynn buys 15 pens from Shop J instead of Shop K
= 480 - 450
= $30

Answer(s): $30