Test Index

WAEC Mathematics 2015 Paper

Question : 1

Total: 45

Solution:

Concept:

Solve the modular congruence and then choose the largest integer in the given range.

Explanation:

Given:

7 + x \equiv 4 \pmod{9}

Subtract 7 from both sides:

x \equiv 4 - 7 \equiv -3 \pmod{9}

Add 9 to the negative remainder:

-3 \equiv 6 \pmod{9}

x \equiv 6 \pmod{9}

, meaning

x

can be

6, 15, 24, \dots

The set is

\{x: 2 \leq x \leq 19,\ x \text{ integer}\}

The values in this range that satisfy the congruence are

6

and

15

The highest value is

15

Answer:

15

(Option C)

Go to Question:

Next Question