The usual price of a marker sold at Shop A and B is $10. During a sale, a discount of 20% is given to every marker sold at Shop A. At Shop B, a discount of 50% is given to the 5th marker for every 5 markers sold. How much cheaper would it be if Penelope buys 13 markers from Shop A instead of Shop B?

	Shop A	Shop B
Price of 1 marker	80%  $8	100% $10
Every 5th marker		50% $5

Price of 1 marker from Shop A in percentage
= 100% - 20%
= 80%

Price of 1 marker from Shop A at 20% discount
= 80% x 10
= ⁸⁰₁₀₀ x 10 
= $8

Cost of 13 markers from Shop A
= 13 x 8
= $104

Price of the 5th marker from Shop B in percentage
= 100% - 50%
= 50%

Cost of 5th marker at Shop B
= 50% x 10
= ⁵⁰₁₀₀ x 10 
= $5

Cost of 1 set of 5 markers at Shop B
= 10 x 4 + 5
= $45

Number of sets of 5 for markers at Shop B
= 13 ÷ 5
= 2 r 3

Cost of 2 sets of 5 markers at Shop B
= 2 x 45
= $90

Cost of 3 markers at Shop B
= 3 x 5
= $15

Cost of 13 markers at Shop B
= 90 + 15
= $105

Amount cheaper if Penelope buys 13 markers from Shop A instead of Shop B
= 105 - 104
= $1

Answer(s): $1