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JAMB Mathematics 1994 Question 23

Question 23

Modular Arithmetic

The multiplication table above has modulo 10 on the set S = {2, 4, 6, 8}, find the inverse of 2.

Diagram for this question
  1. A.2
  2. B.4
  3. C.6
  4. D.8
Show the answer and explanation

Answer: D (8)

Explanation

First find the identity: 6 leaves every element unchanged (e.g. 6 × 4 = 24 ≡ 4). The inverse of 2 is the element that gives 6 with it: 2 × 8 = 16 ≡ 6, so it is 8.