Question

days, x 2 4 6 8
pages, y 80 160 240 320
which of these could be a constant of proportionality.
40 20 80 2

Explanation:

Step1: Recall proportionality formula

For proportional variables $y$ and $x$, $y = kx$, so $k = \frac{y}{x}$.

Step2: Calculate k with first pair

Use $x=2$, $y=80$:
$\frac{80}{2}=40$

Step3: Verify with other pairs

Check $x=4,y=160$: $\frac{160}{4}=40$; $x=6,y=240$: $\frac{240}{6}=40$; $x=8,y=320$: $\frac{320}{8}=40$.

Answer:

40