Question

A bag contains 18 balls out of which x balls are red. a) If one ball is drawn at random from the bag,what is the probability that it is not
red ? b) If two more red balls are put in the bag,the probability of drawing a red ball will be 9/8 times than that in part (a). Find x

Answer 1

Total No . of Obs = 18

No . of Red Balls = x

Probability of Red Ball = Favourable Obs / Total No. of Obs

P(of Red Ball) = x/18

Two Red Balls Are Added

So,

No . of Red Balls = x + 2

Total no .of Balls = 18 + 2 = 20

P(of red Ball) = x + 2 / 20

P given 9 times of P obtained in A

9/8 * x/18 = (x + 2)/20

x / 16 = (x + 2)/20

(x / 16) *  20 = x + 2

5x / 4 = x + 2

5x = 4x + 8

5x - 4x = 8

x = 8

Therefore,

Initial No.Of Red Balls = 8

Answer 2

a)

     18 - x/18

b)  

      x+2/20 = 9/8×(18-x)/18

     

      9x+18 = 180-10x

      x=8