Probability Worksheet Solution7





In this page probability worksheet solution7 we are going to see solution of some practice questions of the probability worksheet.

Question 18

A bag contains 12 balls out of which x balls are white. (i) If one ball is drawn at random, what is the probability that it will be a white ball.(ii) If 6 more white balls are put in the bag and if the probability of drawing a white ball will be twice that of in (i),then find x.

Solution:

Total number of balls = 12

                n (S)  = 12

From this x balls are white in color

(i) Let A  be the event of getting a white ball

n (A) = x

Probability of getting white ball P (A) =  n (A)/n (s)

                                                    = x/12  

(ii) If 6 more white balls are put in the bag and if the probability of drawing a white ball will be twice that of in (i),then find x.

Let B be the event of getting white ball after mixing 6 new white balls.Then  new sample space n (S) = 12 + 6

                                 n (S) = 18

Number of white balls = x + 6

probability of getting white balls = (x + 6)/18

(x + 6)/18 = 2 (x/12)

x + 6/18 = x/6

6(x + 6) = 18 x

6x + 36 = 18 x 

36 = 18x - 6x

 36 = 12 x

 x = 36/12

 x = 3

Number of white balls is 3

Probability of getting white ball = 3/12

                                             = 1/4

Probability of getting white ball = 1/4

Number of white balls = 3


Question 19

Piggy bank contains 100 fifty paise coins, 50 one rupee coins, 20 two rupees coins and 10 five rupee coins. One coin is drawn at random. Find the probability that the drawn coin. (i) Will be fifty paise coin. (ii) Will not be five rupees coin.   

Solution:

Total number of coins = 100 + 50 + 20 + 10

                                   = 180

Sample space n (S) = 180

(i) Will be fifty paise coin

(i) Let A be the event of getting fifty paise coin

n (A) = 100 (Number of fifty paise coin)

P(A) = n (A)/n (S)

        = 100/180

        = 5/9

(ii) Will not be five rupees coin

Let B be the event of not getting five rupees coin

Since it is not five rupee coin,it may be any coin like one rupee coin, two rupees coin and five rupee coins

n (B) = 50 + 20 + 10

         = 80

P (B) = n (B)/n (S)

        = 80/180    

        = 4/9

(i) Will be fifty paise coin, P (A) = 5/9

(ii) Will not be five rupees coin, P (B) = 4/9

probability worksheet solution7 probability worksheet solution7