You borrowed $25 from your friend. you paid him back in full after 6 months. he charged $2 for interest. what was the annual simple interest rate that he charged you?

Annual interest
6 months =1/2 year
so 2 dollars=1/2 of yearly interest
4 dollars is yearly

4 out of 25
4/25 =x%
percent means parts out of 100
x%=x/100
4/25=x/100
multiply both sides 100
16=x

answer is 16%