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Answer: 32
First round:
only even numbers left
Second round:
only multiples of 4 left
Third round:
only multiples of 8 left
Fourth round: Only multiples of 16 will be left
Fifth round: Only multiples of 32 will be left.
32 is the only multiple of 32 under 50, so 32 is the last number left.
Knockdown
Age 11 to 14
ShortChallenge Level 
Answer: 32
First round:
only even numbers leftSecond round:
only multiples of 4 leftThird round:
only multiples of 8 leftFourth round: Only multiples of 16 will be left
Fifth round: Only multiples of 32 will be left.
32 is the only multiple of 32 under 50, so 32 is the last number left.
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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