Final answer:
Kira's annual interest rate is found by dividing the simple interest she received by the product of the principal amount and the time period. After performing the calculation with her values ($120 in interest, $52,000 principal, and 3 years), the annual interest rate is approximately 0.077%.
Step-by-step explanation:
The student is asking how to find the annual interest rate of an investment when the total simple interest received is known, along with the principal amount and the time period. To find the annual interest rate, we can use the simple interest formula:
Simple Interest (I) = Principal (P) × Rate (r) × Time (t)
In Kira's case, she invested $52,000 (Principal, P), for 3 years (Time, t), and received $120 as total simple interest (I). We can rearrange the formula to solve for the Rate (r):
Rate (r) = Simple Interest (I) / (Principal (P) × Time (t))
Insert the known values:
Rate (r) = $120 / ($52,000 × 3)
Now, calculate the rate:
Rate (r) = $120 / $156,000
Rate (r) = 0.00076923...
To express this as a percentage:
Annual interest rate = 0.00076923... × 100%
Annual interest rate = 0.0769%
Thus, the annual interest rate for Kira's investment was approximately 0.077%.