​If mean of a variable X is M, then mean of variable Y = (X – 4)/5 will be:​

Given:
​$$\bar{X} = M, \quad Y = \frac{X - 4}{5} \\[6pt]$$​​
Concept used:
​$$\text{If } Y = aX + b, \text{ then } \bar{Y} = a\bar{X} + b \\[6pt]$$​​
Here, $$a = \frac{1}{5}, \; b = -\frac{4}{5} \\[6pt]$$​​
Formula used:
​$$\bar{Y} = \frac{\bar{X} - 4}{5} \\[6pt]$$​​
Solution:
​$$\text{Substitute } \bar{X} = M: \\[4pt]\bar{Y} = \frac{M - 4}{5} \\[12pt]$$

Correct answer is (b)​​