The usual price of a marker sold at Shop C and D is $20. During a sale, a discount of 15% is given to every marker sold at Shop C. At Shop D, a discount of 30% is given to the 4th marker for every 4 markers sold. How much cheaper would it be if Cindy buys 15 markers from Shop C instead of Shop D?

	Shop C	Shop D
Price of 1 marker	85%  $17	100% $20
Every 4th marker		70% $14

Price of 1 marker from Shop C in percentage
= 100% - 15%
= 85%

Price of 1 marker from Shop C at 15% discount
= 85% x 20
= ⁸⁵₁₀₀ x 20 
= $17

Cost of 15 markers from Shop C
= 15 x 17
= $255

Price of the 4th marker from Shop D in percentage
= 100% - 30%
= 70%

Cost of 4th marker at Shop D
= 70% x 20
= ⁷⁰₁₀₀ x 20 
= $14

Cost of 1 set of 4 markers at Shop D
= 20 x 3 + 14
= $74

Number of sets of 4 for markers at Shop D
= 15 ÷ 4
= 3 r 3

Cost of 3 sets of 4 markers at Shop D
= 3 x 74
= $222

Cost of 3 markers at Shop D
= 3 x 14
= $42

Cost of 15 markers at Shop D
= 222 + 42
= $264

Amount cheaper if Cindy buys 15 markers from Shop C instead of Shop D
= 264 - 255
= $9

Answer(s): $9