The sum of the digits of a large number is 81. using the divisibility rules, by which number or numbers is that large number divisible?
a. only 3
b. 3 and 6
c. 3 and 9
d. 3, 6, and 9

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?