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WAEC Mathematics 2019 Question 5

Question 5

Modular Arithmetic

If 7 + y = 4 (mod 8), find the least value of y, 10 ≤ y ≤ 30.

  1. A.11
  2. B.13
  3. C.19
  4. D.21
Show the answer and explanation

Answer: B (13)

Explanation

y = 4 − 7 = −3 ≡ 5 (mod 8), so y can be 5, 13, 21, 29, … The least value from 10 upwards is 13.