Question
One textbook costs $10 at a shop. During a sale, for every 6 textbooks bought, the 7th textbook can be bought at a discount of 30% off the original price. How many textbooks does Billy buy if he pays $231 altogether?
4 m

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One textbook costs $10 at a shop. During a sale, for every 6 textbooks bought, the 7th textbook can be bought at a discount of 30% off the original price. How many textbooks does Billy buy if he pays $231 altogether?