Question

The coach for a basketball team wants to buy new shoes for her 12 players. Super Sports is offering a 20% discount on each pair of shoes, which were originally priced $72.50. A 6.5% sales tax will be applied to the discounted price. The same shoes are also available on Double Dribble's web site for $54.75. A 9% processing fee will be applied to the cost of the shoes, plus a shipping fee of $5.99 for each pair. What is the difference in the total costs of the 12 pairs of shoes between the two stores?

Answer 1

I am going to show you the easiest, quickest and most direct way of doing it.
Take in account:
1) the result of applying a 20% discount is the same that multiplying times a factor of 0.8, which results from (100 - 20) / 100 = 80 /100 = 0.8
2) adding a 6.5% of tax is the same that multiplyiing by a factor of 1 + 6.5/100 = 1 + 0.065 = 1.065
With that
Super Sport store:
12 * 72.50 * 0.8 * 1.065 = 741.24
Double Dribble
Use that a disscount of 9% results in a factor o 0.91.
I amended the shipping fee data to 5.99 per pair of shoes.
12*54.75*0.91 + 5.99*12 = 669.75
Difference: 741.24 - 669.75 = 71.48