The usual price of a pen sold at Shop Q and R is $20. During a sale, a discount of 25% is given to every pen sold at Shop Q. At Shop R, a discount of 50% is given to the 4th pen for every 4 pens sold. How much cheaper would it be if Jade buys 11 pens from Shop Q instead of Shop R?

	Shop Q	Shop R
Price of 1 pen	75%  $15	100% $20
Every 4th pen		50% $10

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

Price of 1 pen from Shop Q at 25% discount
= 75% x 20
= ⁷⁵₁₀₀ x 20 
= $15

Cost of 11 pens from Shop Q
= 11 x 15
= $165

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

Cost of 4th pen at Shop R
= 50% x 20
= ⁵⁰₁₀₀ x 20 
= $10

Cost of 1 set of 4 pens at Shop R
= 20 x 3 + 10
= $70

Number of sets of 4 for pens at Shop R
= 11 ÷ 4
= 2 r 3

Cost of 2 sets of 4 pens at Shop R
= 2 x 70
= $140

Cost of 3 pens at Shop R
= 3 x 10
= $30

Cost of 11 pens at Shop R
= 140 + 30
= $170

Amount cheaper if Jade buys 11 pens from Shop Q instead of Shop R
= 170 - 165
= $5

Answer(s): $5