Question

y varies indirectly as twice x. When x = 1, y = 3. Find y when x = 4.

Answer 1

"y varies indirectly as twice x" means that \[\Large y = \frac{k}{2x}\]


Now plug in the given info to find k


\[\Large y = \frac{k}{2x}\]


\[\Large 3 = \frac{k}{2(1)}\]


\[\Large 3 = \frac{k}{2}\]


\[\Large 3*2 = k\]


\[\Large 6 = k\]


\[\Large k = 6\]


So the equation is \[\Large y = \frac{6}{2x}=\frac{3}{x}\], which is simply \[\Large y = \frac{3}{x}\]



Now plug in x = 4

\[\Large y = \frac{3}{x}\]


\[\Large y = \frac{3}{4}\]



So when x = 4, y = 3/4