Question

The simple interest, I (in dollars), for a savings

account is jointly proportional to the product of the
time, t (in years), and the principal, P (in dollars).
After three months, the interest on a principal of
$5000 is $106.25. What is the interest after nine
months?

Answer 1

Explanation:

Since the interest is jointly proportional to time and principal, we can write:

I = kPt

where k is the constant of proportionality.

To solve for k, we use the given information that after three months (or 1/4 of a year), the interest on a principal of $5000 is $106.25:

106.25 = k($5000)(1/4)

Solving for k, we get:

k = 0.85

Now we can use this value of k to find the interest after nine months (or 3/4 of a year) on the same principal of $5000:

I = (0.85)($5000)(3/4)

I = $318.75

Therefore, the interest after nine months is $318.75.