A Short Test Of Your Deductive Reasoning
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There are four cards. Each has a number printed on one side and a letter on the other.
There is a rule - which may or may not be true - that every card printed with 'D' on one side must have '3' printed on the other side.
The cards are laid down. They show D, F, 3, 7.
Which card(s) do you have to turn over in order to verify whether or not the rule holds good?
The solution - and the reasoning behind it - is given at around the 3-minute point in the video linked to below.
The answer may surprise you. It certainly suprised me.