Question

Question 64

The variable x varies directly as y and x = 80 when y is 160. What is y when x is 64?

Answer 1

If x varies directly as y.
$\therefore \frac{x}{y}=k$ (constant)...(i)

If x=80 and y =160
$\therefore \frac{x}{y}=\frac{80}{160}=\frac{1}{2}\Rightarrow k=\frac{1}{2}$

When x = 64, then from Eq(i),
$\frac{64}{y}=\frac{1}{2}$ [Putting the value of k]
$\Rightarrow y=64\times 2=128$