Four years ago, a popular sandwich company used to sell 12-inch roast beef subs for only $5, but the same product now costs $7.69. Assuming inflation has been constant those four years, and that the entire cost increase is attributed to inflation, what was the inflation rate?

11.36%

Explanation:

Divide the new price of roast beef with the old one. 7.69 / 5

7.69 : 5 = 1.538

Also divide 1 with the number of years inflation occur

1 : 4 = 0.25

Next, is to raise the first answer gotten to the power of second.

1. 538 ^ 0.25 = 1.113625

Subtract from from 1

1 - 1.1136235 = - 0.1136 = - 11.36%