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JAMB 2001 · UME · Q16

An operation ∗* is defined on the set of real numbers by a∗b=a+b+1a * b = a + b + 1. If the identity element is −1-1, find the inverse of the element 2.

Worked solution (try it first)
  1. The inverse bb of 2 combines with 2 to give the identity −1-1: 2∗b=−12 * b = -1.
  2. Use the rule: 2+b+1=−12 + b + 1 = -1, so b+3=−1b + 3 = -1.
  3. Take 3 from both sides: b=−4b = -4, option A.

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