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JAMB Mathematics 2013 Paper

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Question : 12

Total: 47

P varies jointly as m and u, and varies inversely as q. Given that p = 4, m = 3 and u = 2 and q = 1, find the value of p when m = 6, u = 4 and q =

\frac{8}{5}

12 $\frac{8}{5}$
15
10
28 $\frac{8}{5}$

Solution:

Concept:

Joint and inverse variation combine into a single proportionality constant

k

.

Explanation:

Since

p

varies jointly as

m

and

u

, and inversely as

q

, write:

p = k \cdot \frac{mu}{q}

Substitute

p = 4

,

m = 3

,

u = 2

,

q = 1

:

4 = k \cdot \frac{3 \times 2}{1} = 6k

k = \frac{4}{6} = \frac{2}{3}

So the formula becomes:

p = \frac{2}{3} \cdot \frac{mu}{q}

Now substitute

m = 6

,

u = 4

,

q = \frac{8}{5}

:

p = \frac{2}{3} \times \frac{6 \times 4}{\frac{8}{5}}

p = \frac{2 \times 6 \times 4 \times 5}{3 \times 8}

p = \frac{240}{24} = 10

Answer:

p = 10

Correct option: C.

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