Arithmatical -Probability

DIRECTIONS : Problems based on Probability.
1. In a lottery, there are 10 prizes and 25 blanks. A lottery is drawn at random. What is the probability of getting a prize?
  A.  1/10
  B.  2/5
  C.  2/7
  D.  5/7
Solution
P(getting a prize)= 10 / (10+25)
‹=› 10 / 35
‹=› 2 / 7.
2. A bag contains 6 black and 8 white balls. One ball is drawn at random. What is the probability that the ball drawn is white?
  A.  3/4
  B.  4/7
  C.  1/8
  D.  3/7
Solution
Total number of balls=(6+8)
= 14.
Number of white balls= 8.
P(drawing a white ball)= 8/14
‹=› 4/7.
3. From a pack of 52 cards, two cards are drawn together at random. What is the probability of both the cards being kings?
  A.  1/15
  B.  25/57
  C.  35/256
  D.  1/221
Solution
Let S be the sample space. Then,
n(S) = 52C2= (52×51)/(2×1)
= 1326.
Let E = event of getting 2 kings out of 4.
n(E) = 4C2= (4×4)/(2×1)
= 6.
P(E) = n(E) / n(S) = 6 / 1326
= 1/221.
4. Tickets numbered 1 to 20 are mixed up and then a ticket is drawn at random. What is the probability taht the ticket drawn has a number which is a multiple of 3 or 5?
  A.  1/2
  B.  2/5
  C.  8/15
  D.  9/20
Solution
Here S=(1,2,3,4,5,...,19,20).
Let E=event of getting a multiple of 3 or 5
= (3,6,9,12,15,18,5,10,20)
P(E)= n(E) / n(S)
= 9/20.
5. What is the probability of getting a sum 9 from two throws of a dice?
  A.  1/6
  B.  1/8
  C.  1/9
  D.  1/12
Solution
In two throws of a die, n(S) = (6×6)
= 36.
Let E = event of getting a sum 9= {{3,6),(4,5),(5,4),(6,3)}
P(E)= n(E) / n(S)
= 4/36
‹=›1/9.
Page 1 of 4 1234