Let p: The day is Tuesday. Let q: The day is Thursday.
Let r: She comes to work.

Which represents the statement "The day is Tuesday or Thursday if and only if she comes to work”?

p ↔ (q ∧ r)
p ↔ (q ∨ r)
(p ∧ q) ↔ r
(p ∨ q) ↔ r

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?