In: Statistics and Probability
A trucking company has been requested to quote a realistic turn-around time for a contract to handle the distribution of a certain product to supermarkets around the country. The company provided the following turn-around times for distributing similar goods over a given twelve month period.
Turn-around times in days |
Frequency |
Less than 2 days |
25 |
2 but less than 4 days |
36 |
4 but less than 6 days |
66 |
6 but less than 8 days |
47 |
8 but less than 10 days |
26 |
10 but less than 12 days |
18 |
12 but less than 14 days |
2 |
(a) Calculate the mean turn-around time. [3 marks]
(b) Calculate the standard deviation of the turn-around time. [3 marks]
(c) Calculate the median turn-around time.
Let X= turn around time
Given table can be written as:
Interval | f | X=mid value of interval | X.f | X2*f | cf |
0-2 | 25 | 1 | 25 | 25 | 25 |
2-4 | 36 | 3 | 108 | 324 | 61 |
4-6 | 66 | 5 | 330 | 1650 | 127 |
6-8 | 47 | 7 | 329 | 2303 | 174 |
8-10 | 26 | 9 | 234 | 2106 | 200 |
10-12 | 18 | 11 | 198 | 2178 | 218 |
12-14 | 2 | 13 | 26 | 338 | 220 |
SUM | 220 | 1250 | 8924 |
From the above table we have following: