A sample is selected from one of two populations, S1 and S2, with probabilities P(S1) !.7 and P(S2) !.3. If the sample has been selected from S1, the probability of observing an event A is P(A!S1) !.2. Similarly, if the sample has been selected from S2, the probability of observing A is P(A!S2) !.3. a. If a sample is randomly selected from one of the two populations, what is the probability that event A occurs

Erin bought christmas cards for $2 each to send to her family and friends. which variable is the dependent variable?

X/y + 4y/x divided by x/y - 2y/x explain as in depth as you can how you simplfied the fractions. i don't know where to start on this : /

Assume that there is a 11% rate of disk drive failure in a year. a. if all your computer data is stored on a hard disk drive with a copy stored on a second hard disk drive, what is the probability that during a year, you can avoid catastrophe with at least one working drive? b. if copies of all your computer data are stored on four independent hard disk drives, what is the probability that during a year, you can avoid catastrophe with at least one working drive?