Question: Radioactive substances emit α-particles. The number of such particles reaching a counter over a given time period follows the Poisson distribution, Suppose two substances emit α-particles independently of each other. The first substance gives out α-particles which reach the counter according to the Poisson (3.87) distribution, while the second substance emits α-particles which reach the counter according to the Poisson (5.41) distribution. Find the chance that the counter is hit by at most 4 particles.