1. in a small private school, 4 students are randomly selected from 11 available students. What is the probability that they are the four youngest students?

The probability is?

44..A thief steals an ATM card and must randomly guess the correct four-digit pin code from a 4-key keypad. Repetition of digits is allowed. What is the probability of a correct guess on the first try?The number of possible codes is?

40.Testing for a disease can be made more efficient by combining samples. If the samples from six people are combined and the mixture tests negative, then all six samples are negative. On the other hand, one positive sample will always test positive, no matter how many negative samples it is mixed with. Assuming the probability of a single sample testing positive is 0.2, find the probability of a positive result for six samples combined into one mixture. Is the probability low enough so that further testing of the individual samples is rarely necessary?The probability of a positive test result is?