The mean temperature of Monday to Wednesday was 37°C and of Tuesday to…
2024
The mean temperature of Monday to Wednesday was 37°C and of Tuesday to Thursday was 34°C. If the temperature on Thursday was 4/5 that of Monday, the temperature of Thursday was ___
- A.
36.5°C
- B.
36°C
- C.
35.5°C
- D.
34°C
Attempted by 37 students.
Show answer & explanation
Correct answer: B
Concept: For any n values, mean = sum ÷ n, so sum = mean × n. When two mean-windows overlap on some of the same items, subtracting their sum equations cancels the shared terms and isolates the relationship between the two items that are not shared — here, Monday and Thursday.
Application:
Let Monday's temperature be M and Thursday's be Th, with Th = (4/5)M.
Mean of Monday to Wednesday is 37°C ⇒ M + T + W = 3 × 37 = 111.
Mean of Tuesday to Thursday is 34°C ⇒ T + W + Th = 3 × 34 = 102.
Subtracting the second sum from the first cancels T and W: (M + T + W) − (T + W + Th) = M − Th = 111 − 102 = 9.
Substitute Th = 0.8M into M − Th = 9: M − 0.8M = 0.2M = 9 ⇒ M = 45°C.
Then Th = 0.8 × 45 = 36°C.
Cross-check:
T + W = 111 − 45 = 66, so the Tuesday–Thursday mean is (66 + 36) ÷ 3 = 34°C — matches the given mean.
36 = 0.8 × 45, so the 4/5 ratio between Thursday and Monday also checks out.
Answer: 36°C