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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."
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?