Three flatmates go to buy a kettle
The go into a shop and see one they like for $30
They take the kettle to the counter and pay $10 each
The shop assistant scans the kettle and tells them it's on offer
The kettle only costs $25, so the assistant owes them $5
The shop assistant gives them each $1
He has $2 left over which the men let him keep as a tip
If each flatmate has paid $9 and the shop assistant has $2 where did the other $1 go?
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