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UI Post-UTME Mathematics 2013 Question 6

Question 6

Fractions, Decimals and Approximation

If m and n are distinct natural numbers which of the following is not necessarily a natural number?

  1. A.m + n
  2. B.m2 + n2
  3. C.m − n
  4. D.mn
Show the answer and explanation

Answer: C (m − n)

Explanation

Sums and products of natural numbers are natural, but m − n is negative when m < n (e.g. 2 − 7 = −5).