What is 2/5 subtract 3/10

The probability of winning something on a single play at a slot machine is 0.11. after 4 plays on the slot machine, what is the probability of winning at least once

The standard deviation for a set of data is 5.5. the mean is 265. what is the margin of error?

In a test for esp (extrasensory perception), a subject is told that cards only the experimenter can see contain either a star, a circle, a wave, or a square. as the experimenter looks at each of 20 cards in turn, the subject names the shape on the card. a subject who is just guessing has probability 0.25 of guessing correctly on each card. a. the count of correct guesses in 20 cards has a binomial distribution. what are n and p? b. what is the mean number of correct guesses in 20 cards for subjects who are just guessing? c. what is the probability of exactly 5 correct guesses in 20 cards if a subject is just guessing?