Question

Suppose z varies jointly with x and y. If z = 42 when x = 3 and y = 7, then what is z when x = 7 and y = 8?
Do not include "z =" in your answer.

Answer 1

Since z varies jointly as x and y, the value of z when x = 7 and y= 8 is; 112

According to the question, z varies jointly with X and y.

• In essence, the relationship between z, x and y can be written as;

z = kxy

• where k= constant of proportionality.

We therefore need to find k first, from the first set of values of z, ,x and y.

Then;

• 42 = k × 3 × 7

• k = 42/21

• k = 2.

Consequently, the value of z when x = 7 and y = 8 is as follows;

• z = 2 × 7 × 8.

z = 112.

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