Answer:
To calculate the interest rate that the teenager should charge his sister, we can use the formula:
I = P * r * t
where I is the interest earned, P is the principal (the amount borrowed), r is the interest rate, and t is the time period.
We know that the teenager wants to earn $25 in interest ($75 - $50). We also know that the principal is $50 and the time period is 15 weeks. Plugging these values into the formula, we get:
25 = 50 * r * (15/52)
Solving for r, we get:
r = 13.04%
Therefore, the teenager should charge his sister a simple interest rate of 13.04%. Rounded to the nearest hundredth, this is 13.05%.
hope it helps you