Q22 of 25 Page 15

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.

Given: Total balls = 12


Black balls = x


Concept Used:



Explanation:


Probability of drawing a black ball, P(black)



Now 6 black balls are added to the box, therefore,


Total balls = 12 + 6 = 18


Black balls = x + 6


Let the new probability be P(new)


Now,


P(new) = 2.P(black)


Therefore,




Cross multiplying, we get,


6x + 96 = 18x


18x – 6x = 96


12x = 96


x = 8


Hence, value of x is 8.


More from this chapter

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20

In class, there are 18 girls and 16 boys. The class teacher wants to choose one pupil for a class monitor. What she does, she writes the name of each pupil on a card and puts then into a basket and mixes thoroughly. A child is asked to pick one card from the basket. What is the probability that the name is written on the card is:

(i) the name of a girl


(ii) the name of a boy

 21

Red queens and blackjacks are removed from a pack of 52 playing cards. A card is drawn at random from the remaining cards, after reshuffling them. Find the probability that the card is drawn is

(i) a king


(ii) of red colour


(iii) a face card


(iv) a queen

 23

A bag contains cards numbered from 1 to 49. A card is drawn from the bag at random, after mixing the card thoroughly. Find the probability that the number on the drawn card is

(i) an odd number


(ii) a multiple of 5


(iii) a perfect square


(iv) an even prime number.

 24

(i) Complete the following table:


(ii) A student argues that ‘there are 11 possible outcomes 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and12. Therefore, each of them has a probability . Do you agree with this argument? Justify your answer.