Add mixed-precision decimals carefully: Evaluate 0.6 + 0.66 + 0.066 + 6.606 ensuring correct place-value handling and exact total.

Introduction / Context:
This problem emphasizes accurate addition of decimals having different numbers of digits after the decimal point. A reliable technique is to align decimal points vertically and add place by place to avoid small but costly errors.

Given Data / Assumptions:

• Addends: 0.6, 0.66, 0.066, 6.606
• No rounding is necessary; values are exact.

Concept / Approach:
Keep a consistent number of decimal places by padding with zeros as needed. That allows easy column addition. Alternatively, group numbers to make round figures, but still verify by column addition.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• 6.744 and 6.738: Miss more than one whole unit; likely dropped the 6.606 contribution properly.
• 7.388: Typical carry/column slip when adding 0.66 and 0.066.

Common Pitfalls:

• Failing to align decimals precisely.
• Rounding mid-calculation instead of at the end (not required here).

Final Answer: