Question

The mean of 5 observation is 10 . If mean of first three observations and that of last three is 11 , find third observation .I am a student of class 7​

Answer 1

Number of observations = 5

Sum of observations = ? (Let it be x)

Mean of the data = 10

Thus, x/5=10 => x=5×10=50

Talking about the mean of first three and least three numbers, it is seen that the third and the middle onservation of the array (sequential arrangement) is repeating.

Let the third observation be y.

Now, sum of all observations in this case =

First 3(1ob. + 2ob. +3ob.)+last three(3ob. + 4ob. +5ob.) = x+2y = 50+5y

Total number of observations = 6

Mean of the observations = 11

According to the question, (50+5y)/6=11

=>50+5y=11×6=66

=>5y=66-50=16

=>y=16/5=3.2

Thus, third observation = 3.2

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