The library sells 500 books at its annual used-book fundraiser. They take in a total of $3940. Children's
books cost $5, and adult books cost $9. How many
children's books did they sell?
Let e = number of children's books sold, and Let
a= the number of adult books sold.
Which system of equations can the librarians use to
solve this problem?
A.
5c+9a=500
c+a=3940
c+a=500
C.
5c+9a=3940
B.
a=500-c
9c+5a=3940
a+c=500
D.
5a+9c=3940

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?