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If the witch is guessing, then in the long term, half of the time she will get it right.
So half of the time, she will keep £100, and half of the time, she will have to give the £100 back and pay £50 compensation.
So half of the time, she will make £100. The other half of the time she will lose £50.
This means that after 100 babies have been born, she can expect to have gained £5000 and paid out £2500, so she will be £2500 in profit.
Boy or Girl?
Age 14 to 16
ShortChallenge Level 
If the witch is guessing, then in the long term, half of the time she will get it right.
So half of the time, she will keep £100, and half of the time, she will have to give the £100 back and pay £50 compensation.
So half of the time, she will make £100. The other half of the time she will lose £50.
This means that after 100 babies have been born, she can expect to have gained £5000 and paid out £2500, so she will be £2500 in profit.
You can find more short problems, arranged by curriculum topic, in our short problems collection.
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