Question

If the mean of the observations x, x + 4, x + 5, x + 7, x + 9 is 9, then the mean of the last three observations is:

• A. 7
• B. 10
• C. 11
• D. 8

Answer 1

Answer:

C. 11

Solution: Given : Let the total number be = 5 Mean of the numbers = 9 Calculations : Total sum of the numbers = mean × total numbers ⇒ 9 × 5 ⇒ 45 So, x + x + 4 + x + 5 + x + 7 + x + 9 = 45 ⇒ 5x + 25 = 45 ⇒ x = 4 Now the mean of the last three numbers = sum of the last three numbers/3 sum of last three numbers = x + 5 + x + 7 + x + 9 = 33 Mean = 33/3 ⇒ 11 ∴ Average of last 3 numbers is 11