A study on the use of seat belts versus belted booster seats…

A study on the use of seat belts versus belted booster seats for children ages 4 and 5 reported that “Using seat belts instead of booster seats was associated with increased risk for serious injury in an accident; the relative risk was 2.4.”  Based on this, it can be concluded that for this study:

In an experiment, a person guesses which one of three differ…

In an experiment, a person guesses which one of three different cards a researcher has randomly picked (and hidden from the person who guesses).  This is repeated four times, replacing the cards each time.  Let X = the number of correct guesses in the four tries.  The probability distribution for X, assuming the person is just guessing, is partially provided below. X 0 1 2 3 4 P(X) 0.20 0.39 0.30 0.10   a.   What is the missing probability?   b.   What is the probability that the person would get at least 3 correct guesses?     c.   What is the probability that the number of correct guesses is at most 2?