Question

3 Select the correct answer. The variable y varles directly as x. When x = 20, y= 12. What is the value of y when x= 15?

А. 7 B. 9 C. 18 D. 25 ​

Answer 1

B

Explanation:

Given y varies directly as x, then the equation relating them is

y = kx ← k is the constant of variation

To find k use the condition when x = 20, y = 12, then

12 = 20k ( divide both sides by 20 )

k =
`(12)/(20)` =
`(3)/(5)`

y =
`(3)/(5)` x ← equation of variation

When x = 15, then

y =
`(3)/(5)` × 15 = 9

Answer 2

B.9

Explanation:

What I did is I used ratio.

20:12

15:X

Cross multiply:15x12

Answer:180

The answer you get divided by 20.

180/20=9.