How to find interest using numbers other than 100 and having your answer be a percentage.

To find simple interest, you can use this formula: I=prt. 
I=interest
p=principal
r=rate
t=time (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.