Question

X and y are in direct proportion, when x is 8, y is 12. Which of the following is not a

possible pair of corresponding values of x and y?

a) 10 and 15
b) 2 and 3
c) 6 and 9 d) 15 and 20

Answer 1

d.

Explanation:

if x varies directly as y,

x = ky

8 = 12k

12k = 8

k = 8/ 12

k = 2/3,

x = 2/3 y

now substitute the value of any of the numbers of each pair, and check if it works:

for e.g, find x when y = 15

x = 2/3y

x = 2/3 × 15

x = 10

since you obtain x = 10 when y = 15, the pair is a possible corresponding value of x and y. now do the same for the rest .

ii) x = 2/3y

x = 2/3 × 3, when y = 3

x = 2

hence, this is also a possible pair of x and y values.

iii) x = 2/3y

x = 2/3 × 9 when y = 9

x = 6

again, a possible pair of x and y values.

iv) x = 2/3y

x = 2/3 × 20 when y = 20

x = 40/3

here, when y = 20, x is not 15. it is 40/3.

thus, it can be determined that this is not a possible pair of x and y values.

please try to understand and have a great day!