a)It is conjectured that an impurity exists in 30% of all drinking wells in a certain rural community. In order to gain some insight into the true extent of the problem, it is determined that some testing is necessary. It is too expensive to test all of the wells in the area, so 10 are randomly selected for testing. Find the probability that exactly 3 wells have the impurity.

b)On average, 3 traffic accidents per month occur at a certain intersection. Find the probability that in any given month at this intersection not less than 5 accidents will occur?