Answer: there are 18 dimes and 22 nickels in the collection of 40 coins worth $2.90.
Step-by-step explanation: - 10(40 - n) + 5n = 290
- Distribute the 10: 400 - 10n + 5n = 290
- Combine like terms: -5n = -110
- Divide by -5: n = 22
- d + 22 = 40
- Subtract 22 from both sides: d = 18