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JAMB Mathematics 2024 Paper

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Question : 42

Total: 50

If x is inversely proportional to y and x = 9 when y = 4, find the law containing x and y

x = $\;\frac{16}{y}$
x = $\;\frac{36}{y}$
x = $\;\frac{y}{36}$
x = $\;\frac{13}{y}$

Solution:

Concept:

Inverse proportion means

x = \frac{k}{y}

, where

k

is a constant.

Explanation:

Since

x

is inversely proportional to

y

, write

x = \frac{k}{y}

.

Given

x = 9

when

y = 4

, substitute:

9 = \frac{k}{4}

Multiply both sides by

4

:

k = 9 \times 4 = 36

Now substitute

k = 36

back into the general form:

x = \frac{36}{y}

This is the law connecting

x

and

y

.

Answer:

x = \frac{36}{y}

(Option B).

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