Answer:
8%
Explanation:
For simple interest, we use the equation I = PRT, where I is the interest earned, P is the principal/amount invested, R is the rate as a decimal, not percentage, and T is the time in years.
For this problem, we have to use 0.5 for T, because 6 months is 1/2 a year.
20 = (500)(r)(0.5)
20 = 250r
r = 0.08 = 8%