A trader buys a whole load at one price and sells it in lots at different prices. Every lot but the last is given, and the student works out what the last lot must sell for to reach a stated profit or loss.
It takes several steps: the cost of the whole load, the takings so far, then the shortfall spread over what's left. An early lot always sells below cost, so the answer can't be guessed from the other prices.
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