Case context: When adding decimals, both numbers need the same number of decimal digits. If one number has fewer, add a placeholder zero — this does not change its value, since $0.5 = 0.50$.

Question: You are adding $23.5 + 41.38$. Since 41.38 has two decimal digits and 23.5 has only one, you place a zero after the $5$ in 23.5 before adding. What does 23.5 become, and what is the sum?

Sample answer: 23.5 becomes 23.50. Adding $23.50 + 41.38$ gives $2350 + 4138 = 6488$, so the sum is 64.88.

Key points:

• 23.5 becomes 23.50 because $0.5 = 0.50$
• Both numbers must have the same number of decimal digits before adding
• Adding as whole numbers: $2350 + 4138 = 6488$
• Placing the decimal point gives the final sum 64.88

Rubric: Full credit for correctly writing 23.5 as 23.50 and computing the sum as 64.88. Partial credit if the placeholder step is correct but the addition has an error, or vice versa.