| Want to work with gamma probability | | | | The function returns the value 0.007774. |
| distributions? But a quick explanation is order if | | | | Using the GAMMAINV Fucntion |
| you're not familiar with this powerful statistical | | | | If you have been given a probability and want to |
| concept and technique. Here's the situation: If a | | | | find x, you use the GAMMAINV function,which has |
| Poisson process produces successes at a | | | | the following syntax: |
| constant rate of m per unit of time, then the | | | | =GAMMAINV (probability, alpha, beta) |
| random variable x, the elapsed time until the rth | | | | For example, if the probability equals .5, alpha |
| success, follows the gamma distribution. | | | | equals 8, and beta equals 9, you use the |
| The gamma distribution is often used to | | | | followingformula: |
| determine the amount of time it takes for the rth | | | | =GAMMAINV (.5,8,9) |
| person to arrive in a line. | | | | The function returns the value 69.02. |
| Using the GAMMADIST Function | | | | Using the GAMMALN Function |
| If you know x and want to find the probability, | | | | You use the GAMMALN function to find the |
| you use the GAMMADIST function, whichhas the | | | | natural logarithm of the gamma function, G(x). |
| following syntax: | | | | The GAMMALN function uses the following syntax: |
| =GAMMADIST(x, alpha, beta, cumulative) | | | | =GAMMALN(x) |
| For example, if x equals 25, alpha equals 8, beta | | | | For example, if x equals 25, you use the following |
| equals 9, and cumulatative is TRUE, youuse the | | | | formula: |
| following formula: | | | | =GAMMALN(25) |
| =GAMMADIST (25,8,9,TRUE) | | | | The function returns the value 54.78. |