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

Answer

` (i) ((18-x))/18 (ii) x = 8`

Explanation

(i) Total number of balls = 18.
Number of red balls = x.
Number of balls which are not red = 18 -x.
`:. ` P(getting a ball which is not red) =` (18-x)/18`.
(ii) Now, total number of balls = 18+2 = 20.
Number of red balls now = x +2 .
P(getting a red ball now) = `(x+2)/20 ` and P(getting a red ball in first case) = `x/18`
` rArr (x+2)/20 = 9/8 xx x/18 rArr 144 (x+2) = 180x`
` rArr 180x-144x = 288 rArr 36x = 288 rArr x = (288)/36 = 8`.
Hence, x = 8.