Question : The mean of 20 observations was 42. It was found later that observation 54 was wrongly taken as 45. The corrected new mean is:
Option 1: 45.42
Option 2: 43.5
Option 3: 44.25
Option 4: 42.45
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Correct Answer: 42.45
Solution : The mean of 20 initial observations = 42 Sum of initial observations = 42 × 20 = 840 Wrong entry = 45 Correct entry = 54 Sum after correction = 840 – 45 + 54 = 849 $\therefore$ Final mean = $\frac{849}{20}$ = 42.45 Hence, the correct answer is 42.45.
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Question : The average of 24 observations is 41. The average of the first 9 observations is 42. The average of the last 16 observations is 39. What is the value of the 9th observation?
Option 1: 14
Option 2: 24
Option 3: 18
Option 4: 20
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
Question : The average of 20 numbers is 30 and that of the other 30 numbers is 50. What is the average of all the numbers?
Option 1: 42
Option 2: 47
Option 3: 44
Option 4: 45
Question : Directions: Select the number from among the given options that can replace the question mark (?) in the following series. 48, 54, 45, 51, 42, 48, ?
Option 1: 37
Option 2: 33
Option 3: 39
Option 4: 35
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