Atrain will hold 78 passengers. if it starts out empty and picks up one passenger at the first stop, 2 passengers at the second stop, 3 passengers at the third stop, and so on. after how many stops will it be full?

You were told that the amount of time lapsed between consecutive trades on the new york stock exchange followed a normal distribution with a mean of 15 seconds. you were also told that the probability that the time lapsed between two consecutive trades to fall between 16 to 17 seconds was 13%. the probability that the time lapsed between two consecutive trades would fall below 13 seconds was 7%. what is the probability that the time lapsed between two consecutive trades will be between 14 and 15 seconds?