The usual price of a notebook sold at Shop Y and Z is $30. During a sale, a discount of 20% is given to every notebook sold at Shop Y. At Shop Z, a discount of 30% is given to the 4th notebook for every 4 notebooks sold. How much cheaper would it be if Raeann buys 15 notebooks from Shop Y instead of Shop Z?

	Shop Y	Shop Z
Price of 1 notebook	80%  $24	100% $30
Every 4th notebook		70% $21

Price of 1 notebook from Shop Y in percentage
= 100% - 20%
= 80%

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

Cost of 15 notebooks from Shop Y
= 15 x 24
= $360

Price of the 4th notebook from Shop Z in percentage
= 100% - 30%
= 70%

Cost of 4th notebook at Shop Z
= 70% x 30
= ⁷⁰₁₀₀ x 30 
= $21

Cost of 1 set of 4 notebooks at Shop Z
= 30 x 3 + 21
= $111

Number of sets of 4 for notebooks at Shop Z
= 15 ÷ 4
= 3 r 3

Cost of 3 sets of 4 notebooks at Shop Z
= 3 x 111
= $333

Cost of 3 notebooks at Shop Z
= 3 x 21
= $63

Cost of 15 notebooks at Shop Z
= 333 + 63
= $396

Amount cheaper if Raeann buys 15 notebooks from Shop Y instead of Shop Z
= 396 - 360
= $36

Answer(s): $36