Question

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 look black balls if 6 more black balls are put in the box the probability of drawing a black ball is known double of that it was before find x

Answer 1

Given,
Total number of balls[n(S)] =12
Number of black balls[n(A)]=x

Probability of getting a black ball=n(A)/n(s)

=x/12

Now, six more balls added
Total number of balls =6+12
Here n(S) =18
Black balls added n(B)=6+x

Probability of getting black ball =n(B) / n(S)
=6 +x/18
Now, by given
2[x/12]=6+x/18
2x/12=6+x/18
x/6=6+x/18
18(x)/6=6+x
3x=6+x
3x-x=6
2x=6
x =6/2
x=3