Question

7. A box contains 12 balls of which some are red in colour. If 6 more red balls are
put in the box and a ball is drawn at random, the probability of drawing a red
ball doubles than what it was before. Find the number of red balls in the box​

Answer 1

Solution :-

Let the total number of red balls initially be x

Total number of balls in the box = 12

P(getting a red ball) = x/12

Now, 6 red balls are put in the box, then the total number of balls

= 12 + 6

= 18 balls

Then total number of red balls = (x + 6)

Now,

P(getting a red ball) = (x + 6)/18

According to the question.

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

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

Cross multiplying

⇒ 36x = 12x + 72

⇒ 36x - 12x = 72

⇒ 24x = 72

x = 3

So, initially the number of red balls in the box were 3

Answer.

Answer 2

Answer:

number of red balls are 6+6 = 12 so if it is doubled 12 ×12=144

12+12= 24 balls by 8 is 3