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Q.

A bag contains white, black and red balls only. A ball is drawn at random from the bag. The probability of getting a white ball is 3 10  and that of a black ball is 2 5  . Find the probability of getting a red ball. If the bag contains 20 black balls, then find the total number of balls in the bag.


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a

310, 50  

b

210, 60  

c

310, 30  

d

110, 40   

answer is A.

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Detailed Solution

Given, a bag contains white, black and red balls only. A ball is drawn at random from the bag. The probability of getting a white ball is 3 10   and that of a black ball is 2 5  . The bag contains 20 black balls.
The probability of an event to be occurred is the division of the number of favourable outcomes by the total number of outcomes that is,
Probability of an event =  Number of favourable cases   Total number of cascs   
Determine the probability of getting a red ball by using the formula.
Question Image Determine the value of x by using the formula.
  Probability getting a black ball =  Number of black balls in the bag   Total number of balls  2 5 = 20 x 2x=5×20 x=50   Therefore, the probability of getting a red ball is 310 and  the required number of balls is 50.
Hence, the correct option is 1.
 
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A bag contains white, black and red balls only. A ball is drawn at random from the bag. The probability of getting a white ball is 3 10  and that of a black ball is 2 5  . Find the probability of getting a red ball. If the bag contains 20 black balls, then find the total number of balls in the bag.