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WAEC Mathematics 2020 Paper

Question : 48

Total: 48

Find the least value of x which satisfies the equation 4x = 7(mod 9)

Solution:

Concept:

Solving a linear congruence by adding the modulus to make the right-hand side divisible by the coefficient of

x

Explanation:

Given:

4x \equiv 7 \pmod{9}

We can add

9

7

without changing the congruence because

9 \equiv 0 \pmod{9}

So,

4x \equiv 7 + 9 \pmod{9}

This gives

4x \equiv 16 \pmod{9}

Divide both sides by

4

x \equiv 4 \pmod{9}

The least positive value satisfying this is

x = 4

Answer:

D. 4

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