The usual price of a stapler sold at Shop N and P is $30. During a sale, a discount of 20% is given to every stapler sold at Shop N. At Shop P, a discount of 40% is given to the 5th stapler for every 5 staplers sold. How much cheaper would it be if Erika buys 13 staplers from Shop N instead of Shop P?

	Shop N	Shop P
Price of 1 stapler	80%  $24	100% $30
Every 5th stapler		60% $18

Price of 1 stapler from Shop N in percentage
= 100% - 20%
= 80%

Price of 1 stapler from Shop N at 20% discount
= 80% x 30
= ⁸⁰₁₀₀ x 30 
= $24

Cost of 13 staplers from Shop N
= 13 x 24
= $312

Price of the 5th stapler from Shop P in percentage
= 100% - 40%
= 60%

Cost of 5th stapler at Shop P
= 60% x 30
= ⁶⁰₁₀₀ x 30 
= $18

Cost of 1 set of 5 staplers at Shop P
= 30 x 4 + 18
= $138

Number of sets of 5 for staplers at Shop P
= 13 ÷ 5
= 2 r 3

Cost of 2 sets of 5 staplers at Shop P
= 2 x 138
= $276

Cost of 3 staplers at Shop P
= 3 x 18
= $54

Cost of 13 staplers at Shop P
= 276 + 54
= $330

Amount cheaper if Erika buys 13 staplers from Shop N instead of Shop P
= 330 - 312
= $18

Answer(s): $18