From the calculation done below, the interest when the rate is 9% is $101.25.
<h3>How interest is calculated using direct variation?</h3>
Since the interest on investment varies directly as the rate of interest, the relevant direct variation formula to use to calculate investment is as follows:
i = kr ................................. (1)
Where:
i = interest amount = $45
k = investment = ?
r = interest rate = 0.04
Substituting the values into equation (1) and solving for k, we have:
45 = k0.04
k = 45 / 0.04
k = $1,125
To find the interest when the rate is 9%, we substitute k = $1,125 and r = 9% into equation (1) as follows:
i = $1,125 * 9% = $101.25
Learn more about interest here: brainly.com/question/26457073.
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