What can reduce a person's immune system?

Only 20% of the people in a large city feel that its mass transit system is adequate. If 20 persons are select?

• Only 20% of the people in a large city feel that its mass transit system is adequate. If 20 persons are selected at random, find the probability that 8 or more will feel that the system is adequate. Find the probability that exactly 8 will feel that the system is adequate Round the answers to 3 decimal places The probability that 8 or more will feel that the system is adequate is The probability that exactly 8 will feel that the system is adequate is

• Answer:

  here's how to think about this -- because the population is large relative to the sample size, the proper idea is sampling with replacement [the chance of drawing a person of views X is constant and does not change because you removed someone from the population when you selected them]. this allows you to apply the formulas in your textbook, using 1/5th as the chance of drawing at random a person does responds 'adequate'. Hint: The Poisson distribution deals with scarce events. 1/5th is a scarce event. Off you go to applying the formula for n = 0 through 8 and twenty draws. If you haven't covered that, an approximation would be that the probability of drawing exactly zero such persons would be [1-1/5] ^ 20 and the probability of drawing exactly one such person would be [1-1/5]^19 * [1/5]^1 -- then all you have to do is calculate all the probabilities out through 8; and add up the first seven -- which will be the probability that fewer than 8 are found. enjoy.