The usual price of a pen sold at Shop B and C is $30. During a sale, a discount of 20% is given to every pen sold at Shop B. At Shop C, a discount of 30% is given to the 4th pen for every 4 pens sold. How much cheaper would it be if Anna buys 10 pens from Shop B instead of Shop C?

	Shop B	Shop C
Price of 1 pen	80%  $24	100% $30
Every 4th pen		70% $21

Price of 1 pen from Shop B in percentage
= 100% - 20%
= 80%

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

Cost of 10 pens from Shop B
= 10 x 24
= $240

Price of the 4th pen from Shop C in percentage
= 100% - 30%
= 70%

Cost of 4th pen at Shop C
= 70% x 30
= ⁷⁰₁₀₀ x 30 
= $21

Cost of 1 set of 4 pens at Shop C
= 30 x 3 + 21
= $111

Number of sets of 4 for pens at Shop C
= 10 ÷ 4
= 2 r 2

Cost of 2 sets of 4 pens at Shop C
= 2 x 111
= $222

Cost of 2 pens at Shop C
= 2 x 21
= $42

Cost of 10 pens at Shop C
= 222 + 42
= $264

Amount cheaper if Anna buys 10 pens from Shop B instead of Shop C
= 264 - 240
= $24

Answer(s): $24