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Answer: 2, 4 and 6
Jenny must know for sure that Tom's cards are either both even or both odd.
1 2 3 4 5 6 7
4 odd numbers and 3 even numbers
So Jenny must have taken the 3 evens and left the 4 odds
Jenny's Logic
Age 11 to 14
ShortChallenge Level 
Answer: 2, 4 and 6
Jenny must know for sure that Tom's cards are either both even or both odd.
1 2 3 4 5 6 7
4 odd numbers and 3 even numbers
So Jenny must have taken the 3 evens and left the 4 odds
This problem is taken from the UKMT Mathematical Challenges.
You can find more short problems, arranged by curriculum topic, in our short problems collection.
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