The simple interest i (in dollars) for a savings account is jointly proportional to the product of time (in years) and the principal p (in dollars). after 11 months the interest on a principal of $3970 is $86. what is the constant of the variation

Simple interest I is jointly proportional to the product of time in years and the principal, therefore; mathematically;
I α Pt
introducing a constant;
I = kPt; but I = $ 86, P = $ 3970, while t = 11/12 years
Thus; k = I/Pt
            = 86/ 3970(11/12)
            = 0.0236
Therefore, the constant of the variation is ≈ 0.024

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