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JAMB Mathematics 1994 Question 22

Question 22

Binary Operations

A binary operation * is defined on the set of all positive integers by a*b = ab for all positive integers a, b. Which of the following properties does NOT hold.

  1. A.Closure
  2. B.Associativity
  3. C.Identity
  4. D.Inverse
Show the answer and explanation

Answer: D (Inverse)

Explanation

Products of positive integers are positive integers (closure), multiplication is associative, and 1 is the identity. But the inverse of 2 would be ½, which is not a positive integer.