Chapter 15: Q14P (page 750)
As in Problem , show that the expected number of in n tosses of a die is .
Short Answer
all are equal.
The statement has been proven.
Chapter 15: Q14P (page 750)
As in Problem , show that the expected number of in n tosses of a die is .
all are equal.
The statement has been proven.
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Two decks of cards are “matched,” that is, the order of the cards in the decks is compared by turning the cards over one by one from the two decks simultaneously; a “match” means that the two cards are identical. Show that the probability of at least one match is nearly.
A letter is selected at random from the alphabet. What is the probability that it is one of the letters in the word “probability?” What is the probability that it occurs in the first half of the alphabet? What is the probability that it is a letter after x?
(a) Set up a sample space for the 5 black and 10 white balls in a box discussed above assuming the first ball is not replaced. Suggestions: Number the balls, say 1 to 5 for black and 6 to 15 for white. Then the sample points form an array something like (2.4), but the point 3,3 for example is not allowed. (Why?
What other points are not allowed?) You might find it helpful to write the
numbers for black balls and the numbers for white balls in different colors.
(b) Let A be the event “first ball is white” and B be the event “second ball is
black.” Circle the region of your sample space containing points favorable to
A and mark this region A. Similarly, circle and mark region B. Count the
number of sample points in A and in B; these are and . The region
AB is the region inside both A and B; the number of points in this region is
. Use the numbers you have found to verify (3.2) and (3.1). Also find
and and verify (3.3) numerically.
(c) Use Figure 3.1 and the ideas of part (b) to prove (3.3) in general.
Suppose you have 3 nickels and 4 dimes in your right pocket and 2 nickels and a quarter in your left pocket. You pick a pocket at random and from it select a coin at random. If it is a nickel, what is the probability that it came from your right pocket?
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