The usual price of a pencil sold at Shop G and H is $10. During a sale, a discount of 20% is given to every pencil sold at Shop G. At Shop H, a discount of 30% is given to the 4th pencil for every 4 pencils sold. How much cheaper would it be if Min buys 15 pencils from Shop G instead of Shop H?

	Shop G	Shop H
Price of 1 pencil	80%  $8	100% $10
Every 4th pencil		70% $7

Price of 1 pencil from Shop G in percentage
= 100% - 20%
= 80%

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

Cost of 15 pencils from Shop G
= 15 x 8
= $120

Price of the 4th pencil from Shop H in percentage
= 100% - 30%
= 70%

Cost of 4th pencil at Shop H
= 70% x 10
= ⁷⁰₁₀₀ x 10 
= $7

Cost of 1 set of 4 pencils at Shop H
= 10 x 3 + 7
= $37

Number of sets of 4 for pencils at Shop H
= 15 ÷ 4
= 3 r 3

Cost of 3 sets of 4 pencils at Shop H
= 3 x 37
= $111

Cost of 3 pencils at Shop H
= 3 x 7
= $21

Cost of 15 pencils at Shop H
= 111 + 21
= $132

Amount cheaper if Min buys 15 pencils from Shop G instead of Shop H
= 132 - 120
= $12

Answer(s): $12