I have following statistics problems, could you solve them.
1). If the size of the simple random sample from an infinite population is 25 and the standard error of the mean is 1.22, what must be the size of the sample if the standard error is to be reduced to 0.2.
2). The probability that a computer's monitor will be defective after 20 years is 0.67 and that the computer's CPU will be defective after 20 years is 0.72. Find the probability of (a) both being working well in next 20 years, (b) only monitor working well and (c) at least one working well.
3). Given the probability distribution of X fine the mean and variance of Y-2X-7
Scores 1 2 5 9 11 12
P(x) 0.3 0.1 0.1 0.2 0.1 0.2
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