A man bought a motor cycle for £160.00, sold it for £170.00, then bought it back for £180.00, and finally sold it for £190.00. How much did he make or lose on this series of transactions?
Hint: Imagine starting with £500.
Imagine he started with £500; he bought the bike for £160 leaving him with £340. He then sold it for £170, leaving him with £510. He then bought it again for £180 leaving him £330, and finally he sold it for £190 leaving him with £520, a £20 profit. QED.