Trevor borrows $4000 on a 5-
year loan. He is charged 5%
simple interest per year. How
much interest is he charged
for 5 years?

When rates are expressed as a quantity of 1, such as 2 feet per second or 5 miles per hour, they are called unit rates. if you have a multiple-unit rate such as 120 students for every 3 buses, and want to find the single-unit rate, write a ratio equal to the multiple-unit rate with 1 as the second term.

Whose mistake? can you give more details to what the question is asking?