If the mean of the data 7, 8, 9, 7, 8, 7, λ, 8 is 8, then the variance of this data is?

Mean of the data 7, 8, 9, 7, 8, 7, λ, 8 is 8
∴M = (7+8+9+7+8+7+λ+8)/8 = 8
⇒ 54+λ/8 = 8
⇒ λ = 10
Now, variance σ² is the average of squared difference from mean
So, σ² = (7-8)²+(8-8)²+(9-8)²+(7-8)²+(8-8)²+(7-8)²+(10-8)²+(8-8)²/8
= 1+0+1+1+0+1+4+0/8
= 8/8
= 1
Hence, the variance is 1.