If the mean of six observations 5, 7, 9, α, 11 and 12 is 9, then the value of α is :

Correct option is D

Given:

Observations are 5, 7, 9, α, 11, and 12. The mean of these six observations is 9.

Formula Used:​

​$$\text{Mean} = \frac{\text{Sum of observations}}{\text{Number of observations}}$$​​

Solution :

9 = $$\frac{(5 + 7 + 9 + α + 11 + 12) } 6$$​​

9 = $$\frac{(44 + α) }6$$​​

54 = 44 + α

α = 54 - 44

α = 10

Therefore, the value of α is 10.