1. **Stating the problem:** Three girls initially paid a total of $300 for a motel room ($100 each). Later, they were supposed to be charged only $250, so the clerk gives $50 to the attendant to return to the girls. 2. **What happened next?** The attendant gives $10 back to each girl (total $30), but keeps $20 for himself. 3. **Analyzing the amounts:** - Each girl has now paid $90, totaling $270 ($90 \times 3). - The attendant has $20. 4. **Where is the mistake?** Adding the $270 paid and the $20 kept by the attendant as $270 + $20 = $290 is incorrect, because the $20 is part of the $270, not in addition to it. 5. **Correct interpretation:** - The $270 the girls paid includes the $250 for the room plus the $20 kept by the attendant. - Mathematically: $$270 = 250 + 20$$ - The $30 returned to the girls ($10 each) plus the $270 they paid equals the original $300. 6. **Summary:** The error is in the misleading addition of $20 to $270; the $20 is already included in the $270 total payment, so there's no missing $10.