The usual price of a file sold at Shop S and T is $40. During a sale, a discount of 20% is given to every file sold at Shop S. At Shop T, a discount of 50% is given to the 7th file for every 7 files sold. How much cheaper would it be if Xandra buys 16 files from Shop S instead of Shop T?

	Shop S	Shop T
Price of 1 file	80%  $32	100% $40
Every 7th file		50% $20

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

Price of 1 file from Shop S at 20% discount
= 80% x 40
= ⁸⁰₁₀₀ x 40 
= $32

Cost of 16 files from Shop S
= 16 x 32
= $512

Price of the 7th file from Shop T in percentage
= 100% - 50%
= 50%

Cost of 7th file at Shop T
= 50% x 40
= ⁵⁰₁₀₀ x 40 
= $20

Cost of 1 set of 7 files at Shop T
= 40 x 6 + 20
= $260

Number of sets of 7 for files at Shop T
= 16 ÷ 7
= 2 r 2

Cost of 2 sets of 7 files at Shop T
= 2 x 260
= $520

Cost of 2 files at Shop T
= 2 x 20
= $40

Cost of 16 files at Shop T
= 520 + 40
= $560

Amount cheaper if Xandra buys 16 files from Shop S instead of Shop T
= 560 - 512
= $48

Answer(s): $48