simple interest.

Question

alberto invests his $90 for 2 years at r% per year simple interest. at the end of 2 years the amount of money he has is $99. calculate the value of r%.

Answer 1

A = p(1 + rt)

99 = 90(1 + 2r)

99/90 = (1 + 2r)

11/10 = 1 + 2r

1/10 = 2r

1/20 = r

5% = r

 

Answer 2

He makes 9/90 = 10% in 2 years? That means the rate is 10/2 = 5%.