At the clothing store where you work, T-shirts are on sale, 3 for $10. A customer at the store says that one T-shirt should cost $7 at this rate. What error did the customer make?

The customer divided 10 by 3 instead of dividing 3 by 10.
The customer divided 3 by 10 instead of dividing 10 by 3.
The customer subtracted 3 from 10 instead of dividing 10 by 3.
The customer added 10 and 3 instead of dividing 3 by 10.
The customer subtracted 3 from 10 instead of dividing 3 by 10.