A box contains balls out of whichare black. If one ball is drawn at random from the box, what is the probability that it will be a black ball? If more black balls are put in the box, the probability of drawing a black ball is now double of what it was before. Find.
Given that, number of black balls
and total number of balls
So, the required probability is
When 6 more black balls are put in the box, total number of balls then
Number of black balls
And probability of black ball is
as per condition
Hence, number of black balls