If a number is divisible by 6, it is divisible by 3. The number 21 is divisible by 3. What follows?

Answer and explanation

Correct answer: D. We cannot tell whether 21 is divisible by 6 from the rule alone.

  1. Step 1: The rule says 6 implies 3, not the other way round. Step 2. Knowing 21 is divisible by 3 gives no information about 6 from the rule alone. Answer: We cannot tell whether 21 is divisible by 6 from the rule alone. Why not the others: 21 must be divisible by 6.: This reverses the rule. 21 cannot be divisible by 6.: This is not supported by the rule. 21 is not divisible by 2 and so fails the rule.: This is true as a fact but does not follow from the rule given.

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