Test Index

WAEC Mathematics 2020 Paper

© africaexams.com

Question : 15

Total: 48

Given that x is directly proportional to y and inversely proportional to Z, x = 15 when y = 10 and Z = 4, find the equation connecting x, y and z

x = $\; \frac{6y}{z}$
x = $\; \frac{12y}{z}$
x = $\; \frac{3y}{z}$
x = $\; \frac{3y}{2z}$

Solution:

Concept:

Combined variation:

x

varies directly as

y

and inversely as

z

.

Explanation:

From the relation,

x \propto \frac{y}{z}

.

Convert the proportion to an equation using a constant

k

:

x = \frac{ky}{z}

.

Substitute the given values:

x = 15

,

y = 10

,

z = 4

.

15 = \frac{10k}{4}

.

Multiply both sides by 4:

60 = 10k

.

Divide both sides by 10:

k = 6

.

Therefore, the equation connecting

x

,

y

, and

z

is:

x = \frac{6y}{z}

.

This matches option A.

Answer:

x = \frac{6y}{z}

Option A.

© africaexams.com

Go to Question:

Prev Question

Next Question