Question:
If the mean of the observations: x 1, x 4, x 5, x 8, x 11 is 10, the mean of the last three observations is (A) 12.5 (B) 12.2 (C) 13.5 (D) 14.2
Answer:
Given data is : x+1, x+4, x+5, x+8, x+11
Mean = (x+1 + x+4 + x+5 + x+8 + x+11)/5
=>10 = (5x + 29)/5
=> 10*5 = 5x + 29
=>50 = 5x + 29
=> 5x = 50-29
=> 5x = 21
=> x = 21/5
=> x = 4.2
Mean of last three observations = (x+5 + x+8 + x+11)/3
= (3x + 24)/3
= x + 8
= 4.2 + 8 (By putting value of x)
= 12.2
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