Given:
- The relationship between variables x and y is given as 2x - 3y - 7 = 0.
- The mean of x is 1.
- The mean deviation about the mean of x is 0.3.

To Find:
The coefficient of mean deviation of y about its mean.

Explanation:
Mean of x:
The mean of x is given as 1.

Mean Deviation about Mean of x:
Mean deviation about the mean is a measure of dispersion. It is calculated by taking the absolute difference between each value and the mean, summing them up, and dividing by the number of values.
In this case, the mean deviation about the mean of x is given as 0.3.

Equation of the Relationship:
The given relationship between x and y is 2x - 3y - 7 = 0.
We can rewrite this equation as 2x - 3y = 7.

Finding the Mean of y:
To find the mean of y, we need to rearrange the equation in terms of y:
2x - 3y = 7
-3y = -2x + 7
y = (2/3)x - 7/3

Mean Deviation about Mean of y:
The mean deviation about the mean of y can be calculated using the following formula:
Mean deviation about mean = Σ|y - mean of y| / n

Substituting the Values:
We know that the mean of x is 1 and the mean deviation about the mean of x is 0.3.
Substituting these values into the equation, we get:
0.3 = Σ|y - (2/3)x - 7/3| / n

Simplifying the Equation:
To simplify the equation, we need to find the sum of |y - (2/3)x - 7/3|.
Since the equation of the relationship is 2x - 3y = 7, we can substitute y with (2/3)x - 7/3 in the absolute value expression:
|y - (2/3)x - 7/3| = |(2/3)x - 7/3 - (2/3)x - 7/3| = |0| = 0

Conclusion:
Since the absolute value of y - (2/3)x - 7/3 is always 0, the mean deviation about the mean of y is also 0.
Therefore, the coefficient of mean deviation of y about its mean is 0.