Interest varies jointly with time and principle
let I = interest
time = t
Principle = P
Mathematically:
[tex]\begin{gathered} I\text{ }\alpha\text{ tP} \\ I\text{ = ktP} \\ where\text{ k = constant of proportionality} \end{gathered}[/tex]when interest = 1000
time = 10 years
Principal = 6000
We will substitute these values in the formula we got above to get k:
[tex]\begin{gathered} 1000\text{ = k}\times10\times6000 \\ 1000\text{ = 60000k} \\ divide\text{ both sides by 60000:} \\ \frac{1000}{60000}\text{ = }\frac{60000k}{60000} \\ k\text{ = 1/60} \end{gathered}[/tex]To get the equation of the variable, we will substitute the value of k in the formula:
[tex]\begin{gathered} I\text{ = }\frac{1}{60}\times t\times P \\ \\ Equation\text{ of the variable:} \\ I\text{ = }\frac{tP}{60} \end{gathered}[/tex]