Call the standard wrench S and the four other wrenched A, B, C, and D.
Weigh AB vs CS
Case 1: AB equals CS
Weigh S vs D: If S equals D then none are defective. If S is heavier than D then D is defective and light. If S is lighter than D then D is defective and heavy.
Case 2: AB is heavier than CS
Weigh A vs B: If A is heavier than B then A is defective and heavy, If A is lighter than B then B is defective and heavy, If A equals B then C is defective and light.
Case 3 AB is lighter than CS
Weigh A vs B: If A is heavier than B then B is defective and light, If A is lighter than B then A is defective and light, If A equals B then C is defective and heavy. |