statistics 問題

阿sa

The number, X, of fatal accidents occur at random at a known "black spot" is a Poisson process with mean 4 per yr.

The number, Y, of non-fatal accidents at the same place may be assumed to be Poisson random variable with mean 12 per year, and X and Y are independent.

1. State the distribution of V=X+Y and write down the mean and variance of V

2. Given that there were in total 20 accidents one year, find the probability that 5 of  these were fatal