Adalberto has $2.25 in dimes and nickels. He has nine more nickels than dimes. Solving 0.10d + 0.05(d + 9) = 2.25 gives which number of dimes?

1. Distribute the 0.05 across the parentheses: 0.10d plus 0.05d plus 0.45 equals 2.25. 2. Combine the like terms on the left: 0.15d plus 0.45 equals 2.25. 3. Subtract 0.45 from both sides: 0.15d equals 1.80. 4. Divide both sides by 0.15: d equals 12. 5. Checking, 12 dimes is worth $1.20 and 21 nickels (nine more than 12) is worth $1.05, and 1.20 plus 1.05 equals $2.25. 6. Reading the number of nickels, 21, as the answer instead of the number of dimes is the trap this question is built to catch, since the equation was set up to solve for d, the dimes. _Source: OpenStax Prealgebra (CC BY 4.0), Ch 9 "Math Models and Geometry", section 9.2 Solve Money Applications_