A box contains 12 balls out of which x are black. If one ball is drawn at random from the box, what is the probability that it will be a black ball?
If 6 more black balls are put in the box, the probability of drawing a black ball is now double of what it was before. Find x.
Total number of balls = 12
Total number of black balls = x
$\mathrm{P}($ getting a black ball $)=\frac{x}{12}$
If 6 more black balls are put in the box, then
Total number of balls = 12 + 6 = 18
Total number of black balls = x + 6
$\mathrm{P}($ getting a black ball now $)=\frac{x+6}{18}$
According to the condition given in the question,
$2\left(\frac{x}{12}\right)=\frac{x+6}{18}$
$3 x=x+6$
$2 x=6$
$x=3$
Click here to get exam-ready with eSaral
For making your preparation journey smoother of JEE, NEET and Class 8 to 10, grab our app now.