Logical cards
Problem
A set of five cards each have a letter printed on their front and a number printed on their back, as follows:
Which one of the five cards provides a counter example to the statement "Every card that has a vowel on its front side has an even number on its back."
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If you enjoyed this problem, you might like to try this one (which comes from Foundation Assignment 4 from the STEP Support Programme):
I have 4 double-sided cards in front of me, each has a number on one side and a letter on the other. The faces that are up are showing “6”, “E”, “Q” and “7”.
I claim that if there is an even number on one side of the card then there is a vowel on the other. Which cards do you need to turn over in order to check my claim?
Student Solutions
Well done to Yazan from Dubai International Academy in the United Arab Emirates who sent in this solution and explanation:
The answer for the question is A, because the term “counter” means opposite, and the opposite of even numbers are odd numbers, so we have to find a vowel on the front with an odd number on the back. To remember, here are the fronts and backs of each card:
Front: A Back: 3
Front: B Back: 4
Front: C Back: 1
Front: D Back: 7
Front: E Back: 8
The vowels are A and E. Card E has the number 8 on the back, but it is even, which means Card E can’t be the answer, however card A has 3 on the back and 3 is odd, therefore, card A is correct.