In: Accounting
Cars arrive at Carla’s Muffler Shop for repair work at an average of 3 per hour, following an exponential distribution. (a) What is the expected time between arrivals? (b) What is the variance of the time between arrivals?
Use Appendix C

Formula sheet
| A | B | C | D | E | F | G |
| 2 | ||||||
| 3 | Exponential Distribution function is given by following formula: | |||||
| 4 | ||||||
| 5 | f(x) = ?e-?x | |||||
| 6 | ||||||
| 7 | Where: | |||||
| 8 | ?: The rate parameter of the distribution, = 1/µ (Mean) | |||||
| 9 | f(x): Exponential probability density function | |||||
| 10 | x: Random variable | |||||
| 11 | ||||||
| 12 | Mean of exponential function | =1/? | ||||
| 13 | Variance of exponential function | =1/?2 | ||||
| 14 | ||||||
| 15 | Since ? is the rate parameter, car arriving at the rate of 3 per hour is ?. | |||||
| 16 | ?= | 3 | Per hour | |||
| 17 | ||||||
| 18 | a) | |||||
| 19 | ||||||
| 20 | Expected time between arrival | =Mean of exponential distribution | ||||
| 21 | =1/ ? | |||||
| 22 | =1/D16 | hours | ||||
| 23 | =D22*60 | min | ||||
| 24 | ||||||
| 25 | Hence Expected time between arrival | =D23 | min | |||
| 26 | ||||||
| 27 | b) | |||||
| 28 | ||||||
| 29 | Variance of exponential function | =1/?2 | ||||
| 30 | =1/(D16^2) | =1/(D16^2) | ||||
| 31 | ||||||
| 32 | Hence Variance of time between arrival is | =D30 | ||||
| 33 | ||||||