The usual price of a file sold at Shop T and U is $10. During a sale, a discount of 20% is given to every file sold at Shop T. At Shop U, a discount of 50% is given to the 4th file for every 4 files sold. How much cheaper would it be if Gwen buys 14 files from Shop T instead of Shop U?

	Shop T	Shop U
Price of 1 file	80%  $8	100% $10
Every 4th file		50% $5

Price of 1 file from Shop T in percentage
= 100% - 20%
= 80%

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

Cost of 14 files from Shop T
= 14 x 8
= $112

Price of the 4th file from Shop U in percentage
= 100% - 50%
= 50%

Cost of 4th file at Shop U
= 50% x 10
= ⁵⁰₁₀₀ x 10 
= $5

Cost of 1 set of 4 files at Shop U
= 10 x 3 + 5
= $35

Number of sets of 4 for files at Shop U
= 14 ÷ 4
= 3 r 2

Cost of 3 sets of 4 files at Shop U
= 3 x 35
= $105

Cost of 2 files at Shop U
= 2 x 5
= $10

Cost of 14 files at Shop U
= 105 + 10
= $115

Amount cheaper if Gwen buys 14 files from Shop T instead of Shop U
= 115 - 112
= $3

Answer(s): $3