Question

9. If y varies directly with x and y = -3 when x = 6, find y when x = 14.

Answer 1

9)

If y varies directly with x and y = -3 when x = 6, find y when x = 14.

We know if y varies directly with x, we get the equation

y ∝ x

y = kx

k = y/x

where k is called the constant of variation.

we are given y = -3 when x = 6

so substitute y = -3 and x = 6 to determine 'k'

k = y/x

k = -3/6 = -1/2

Now we have to find y when x = 14

so substituting x = 14 and k = -1/2 to find y

y = kx

y =  -1/2 × 14 = -7

Therefore, the value of y = -7 when x = 14

10) If y is directly proportional to x and y = 4 when x = 3, find x when y = -12.

we are given y = 4 when x = 3

so substitute y = 4 and x = 3 to determine 'k'

k = y/x

k = 4/3

Now we have to find x when y = -12

so substituting y = -12 and k = 4/3 to find x

y = kx

x = y/k

x = [-12] / [4/3] = [-12×3] / [4]

x = -36/4

x = -9

Therefore, the value of x = -9 when x = 3

11)

If y varies directly with x and y = -6 when x = 2, find the constant of variation.

We are given

y = -6

x = 2

so substitute y = -6 and x = 2 in the equation

k = y/x

k = -6/2

k = -3

Therefore, the value of the constant of variation will be:

• k = -3