Question

A hardware store sells hammers for $8.29 each and boxes of nails for $4.99 each. A convenience store sells the same hammer for $6.79 each and the same box of nails for $5.49 each. Matrix C, shown below, represents the prices of a hammer and a box of nails at the two stores.

c= 8.29    4.99

     6.79    5.49

The two stores are located in a county with an 8% sales tax. Matrix C' represents the costs of a hammer and a box of nails at the two stores including sales tax, in dollars. Which of these is the correct representation of matrix C'?

Answer 1

Multiply every price by 1.08 (add 8% tax). So C' = 1.08C:

C' = [ [8.29·1.08, 4.99·1.08],
[6.79·1.08, 5.49·1.08] ]
= [ [8.9532, 5.3892],
[7.3332, 5.9292] ]
≈ [ [8.95, 5.39],
[7.33, 5.93] ] (dollars).