In: Statistics and Probability
Solution- To find Poisson distribution probabilities in Excel, use the function =POISSON(x;λ;0)
x=number of occurrences over a specified interval
λ=average number of occurrences over a specified interval = 20
since the probability distribution in excel for an interval of 30 minute duration given below.
| x | p(X=x) | Round off at six places | 
| 0 | 2.06115E-09 | 0 | 
| 1 | 4.12231E-08 | 0 | 
| 2 | 4.12231E-07 | 0 | 
| 3 | 2.7482E-06 | 0.000003 | 
| 4 | 1.3741E-05 | 0.000014 | 
| 5 | 5.49641E-05 | 0.000055 | 
| 6 | 0.000183214 | 0.000183 | 
| 7 | 0.000523468 | 0.000523 | 
| 8 | 0.001308669 | 0.001309 | 
| 9 | 0.002908153 | 0.002908 | 
| 10 | 0.005816307 | 0.005816 | 
| 11 | 0.010575103 | 0.010575 | 
| 12 | 0.017625171 | 0.017625 | 
| 13 | 0.027115648 | 0.027116 | 
| 14 | 0.03873664 | 0.038737 | 
| 15 | 0.051648854 | 0.051649 | 
| 16 | 0.064561067 | 0.064561 | 
| 17 | 0.075954196 | 0.075954 | 
| 18 | 0.084393552 | 0.084394 | 
| 19 | 0.088835317 | 0.088835 | 
| 20 | 0.088835317 | 0.088835 | 
| 21 | 0.084605064 | 0.084605 | 
| 22 | 0.076913695 | 0.076914 | 
| 23 | 0.066881474 | 0.066881 | 
| 24 | 0.055734561 | 0.055735 | 
| 25 | 0.044587649 | 0.044588 | 
| 26 | 0.034298192 | 0.034298 | 
| 27 | 0.025406068 | 0.025406 | 
| 28 | 0.018147191 | 0.018147 | 
| 29 | 0.012515304 | 0.012515 | 
| 30 | 0.008343536 | 0.008344 | 
probability that no more then 14 customers will arrive = P(X<_14)
= probability sum of 0 to 14 of above table.
= 0.104864