Question

If i put $1500 into my savings account and earned $180 of interest at 4% simple interest, how long was my money in the bank

Answer 1

The "interest" is always the annual rate, that is, 4% for a year.

The percent of interest you earned is  (180/1500) = 0.12  =  12% .

Since you got 4% per year, your money was in the bank for

                     (12 %) x (1 year / 4%)

                 =    (12 x 1 / 4)  (% / %) (year)  =  3 years .