Mean Deviation about Mean:
Mean deviation about mean is used to measure the average distance of each observation from the mean of the set of observations.

Calculation of Mean:
To calculate the mean of the given observations, we need to add all the observations and divide the sum by the total number of observations.
Mean = (50+60+50+50+60+60+60+50+50+50+60+60+60+50)/14
Mean = 55

Calculation of Deviation:
Deviation is the difference between each observation and the mean of the set of observations.
Deviation for each observation can be calculated by subtracting the mean from each observation.
Deviation = Observation - Mean

Calculation of Mean Deviation about Mean:
Mean deviation about mean is calculated by taking the mean of the absolute values of the deviations from the mean.
Mean deviation about mean = Sum of |Deviation| / Total number of observations

To calculate the mean deviation about mean for the given observations, we need to follow the below steps:
1. Calculate the deviation for each observation by subtracting the mean from each observation.
2. Calculate the absolute value of each deviation.
3. Add all the absolute deviations and divide the sum by the total number of observations.

Deviation for each observation can be calculated as follows:
50-55 = -5
60-55 = 5
50-55 = -5
50-55 = -5
60-55 = 5
60-55 = 5
60-55 = 5
50-55 = -5
50-55 = -5
50-55 = -5
60-55 = 5
60-55 = 5
60-55 = 5
50-55 = -5

Absolute deviation for each observation can be calculated by taking the absolute value of each deviation.
|Deviation| for each observation can be calculated as follows:
| -5 | = 5
| 5 | = 5
| -5 | = 5
| -5 | = 5
| 5 | = 5
| 5 | = 5
| 5 | = 5
| -5 | = 5
| -5 | = 5
| -5 | = 5
| 5 | = 5
| 5 | = 5
| 5 | = 5
| -5 | = 5

Now, we need to add all the absolute deviations and divide the sum by the total number of observations.
Mean deviation about mean = Sum of |Deviation| / Total number of observations
Mean deviation about mean = (5+5+5+5+5+5+5+5+5+5+5+5+5+5)/14
Mean deviation about mean = 35

Therefore, the value of mean deviation about mean for the given observations is 35. Hence option (c) is the correct answer.