Question

Three friends bought 4, 6, and 8 books. The table shows the cost of the books.

Number of Books 4 6 8
Cost ($) 30 45 60
What is the constant of proportionality?

A. 2

B.7.5

C.15

D.30

Answer 1

B.

Step-by-step explanation:

I took the K12 test so the answer above is correct

Answer 2

Option (B) is correct .

The constant of proportionality is 7.5 .

Reason

Let us assume that the number of books be x.

Let us assume that the cost of books be y .

Than

`y \propto x`

y = kx

Where k is constant of proportionality .

As given

Number of Books 4 6 8

Cost ($) 30 45 60

Thus

when x = 4 , y = 30

Put in the equation y = kx .

`30 = 4k`

`k = (30)/(4)`

k = 7.5

when x = 6 , y = 45

Put in the equation y = kx .

`45 = 6k`

`k = (45)/(6)`

k = 7.5

when x = 8 , y = 60

Put in the equation y = kx .

`60 = 8k`

`k = (60)/(8)`

k = 7.5

Therefore the constant of proportionality is 7.5 i.e option (B) is correct .