Question

If $d$ varies directly as the square of $t$ and if $d=18$, when $t=3$, the value of $d$ when $t=5$ is

• A. 40
• B. 45
• C. 50
• D. 55
• E. 60

Answer 1

The correct option is C 50

Given, $d$ varies directly with square of $t$, which implies $d\propto t^2$
Let the proportionality constant be $k$, we have $d=k{t}^2$
At $d=18$, then $t=3$
We get $18=k\times 9$, which implies $k=2$
Therefore the equation is $d=k{t}^2$
At $t=5$, we get $d=50$