Test Index

WAEC Mathematics 2015 Paper

Question : 11

Total: 45

Solution:

Concept:

Translate the given condition into a quadratic equation and take the positive root.

Explanation:

Let the given positive number be

x

According to the question:

x + 42 = x^2

Rearrange the equation:

x^2 - x - 42 = 0

Factorise the quadratic:

(x - 7)(x + 6) = 0

Therefore:

x = 7 \quad \text{or} \quad x = -6

Since the number is positive, reject

x = -6

Answer:

The number is

7

Option C.

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