Question : The mean height of 30 students was given as 140 cm. It was later observed that one of the observations was incorrectly copied as 121 cm while it was 134 cm. What was the correct mean height? [Give your answer correct to one place of decimal.]
Option 1: 150.4 cm
Option 2: 140.4 cm
Option 3: 160.4 cm
Option 4: 130.4 cm
Correct Answer: 140.4 cm
Solution :
The mean height of 30 students = 140 cm
Sum of heights = 140 × 30 = 4200
Actual sum of heights = 4200 – 121 + 134 = 4213
Actual mean height = $\frac{4213}{30}$ = 140.43
Hence, the correct answer is 140.4 cm.
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