Brain Teasers
Mental Money
If I lost 50% of all my money and then regained 50% but am now $50 off my old total, what was my old total?
Answer
$200Since you don't know if you end up $50 more or $50 less than your old total, you have to try each of two equations:
1) 0.5*X + 0.5*(0.5*X) = X - 50
2) 0.5*X + 0.5*0.5*X = X + 50
Where X is the original amount.
The answer to (1) is X = 200 and the answer to (2) is X = -200. Obviously he couldn't have started with -$200, so the answer must be $200.
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