Weekly temperature: The average of the first three days is 27 C and of the next three days is 29 C. If the average temperature for the entire 7 day week is 28.5 C, find the temperature on the last day.

Introduction / Context:
Average over the whole equals total for the week divided by 7. Given two three day blocks, the seventh day is the remainder when those are removed from the total.

Given Data / Assumptions:

• First 3 day average = 27 C
• Next 3 day average = 29 C
• Weekly average = 28.5 C

Concept / Approach:
Compute totals for each block and subtract from the weekly total.

Step-by-Step Solution:

Verification / Alternative check:
Average recomputed equals 28.5 C when all seven are used.

Why Other Options Are Wrong:

• 10.5 C, 21 C, 42 C: Do not satisfy the computed remainder.

Common Pitfalls:
Using 6 days mistakenly for the weekly total or mixing Celsius symbols with arithmetic and rounding.

Final Answer: