SAT Mc Graw Hill 2011

356 MCGRAW-HILL’S SAT

SAT Practice 6: Probability Problems

1. The figure above shows a spinner in the mid-
   dle of a disc divided into six equal parts, each
   labeled with a number. What is the probabil-
   ity that the spinner will land on a number that
   is either even or greater than 5?

(A) (B) (C)

(D) (E)

2. A jar contains 10 blue marbles, 8 green marbles,
   and 14 red marbles. How many green marbles
   must be added so that the probability
   of choosing a green marble at random is?
   (A) 16 (B) 32 (C) 40
   (D) 64 (E) 72


3. A fair six-sided die has faces bearing the numbers
   1, 2, 3, 4, 5, and 6. When the die is thrown, the
   numbers on the five visible faces are added. What
   is the probability that this sum is greater than 18?

(A) (B) (C)

(D) (E)

4. A target consists of three concentric circles,
   with radii of 1 meter, 2 meters, and 3 meters.
   If an arrow that hits the target hits any point
   on the target with equal probability, what is
   the probability that an arrow that hits the tar-
   get falls in the outermost region (between the
   second and third circles)?

(A) (B) (C)

(D) (E)

5

9

4

9

π

9

1

3

1

9

5

6

2

3

1

2

1

3

1

6

3

4

5

6

2

3

1

2

1

3

1

6

5. The probability of a meteor shower occurring in
   the skies above a particular island on any
   given night is. Independently, the proba-
   bility that any given night will be cloudless is
   . What is the probability that, on any given
   night, there will be a meteor shower andit will
   be cloudless?

(A) (B) (C)

(D) (E)

6. A basket contains red, green, and yellow balls,
   all of equal size. The probability of choosing a
   green ball at random is. If there are 3 times
   as many red balls as yellow balls, what is the
   probability of choosing a yellow ball at random?


7. A certain disease occurs in 1 person out of
   every 101 people. A test for the disease is 100%
   accurate for patients with the disease and 99%
   accurate for patients without it. That is, it
   gives a “false positive” 1% of the time even if
   the person tested doesn’t have the disease. If
   you take this test and it returns a positive re-
   sult, what is the probability that you have the
   disease?
   (A) 1 (B) .99 (C) .95
   (D) .50 (E) .01

....

1 2 3 4 5 7 8 9

6

1

0 2 3 4 5 7 8 9

6

1

0 2 3 4 5 7 8 9

6

1

0 2 3 4 5 7 8 9

6

4

7

8

25

4

25

17

200

3

100

1

50

1

4

2

25

5

9

2

8

3

6