Question

A bag contains 20 balls out of which X balls are red 1) if one ball is drawn at random from the bag what is the probability that it is not read (2) if 4 more red balls are put in the bag the probability of drawing a red ball will be 5/4 times the probability of drawing a red ball in First case , find the value of x

Answer 1

Solution-:
Total No . of Obs = 20
No . of Red Balls = x
Probability of Red Ball = Favourable Obs / Total No. of Obs
P(of Red Ball) = x/20

Four Red Balls Are Added
So,
No . of Red Balls = x + 4
Total no .of Balls = 20 + 4 = 24
P(of red Ball) = x + 4 / 24
P given 5/4 times of P obtained in A

5/4 * x/20 = (x + 4)/24
x / 16 = (x + 4)/24
(x / 16) * 24 = x + 4
24x / 8 = x + 4
3x/2=x+4
3x = 2x + 8
3x - 2x = 8
x = 8
Hence number of red balls = 8