an urn 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 no. of balls in the bag.
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Let the total no. of balls be x
Probability of drawing a black ball = 2/5 (given)
20/x = 2/5
x = 50 = no.of balls
Let no. of white balls be y
Now Probability of getting a white ball = 3/10 (given)
y/50 = 3/10
y = 15
Thus,No.of red balls = 50-(20+15)
= 50-35
= 15
Therefore, Probability of getting a red ball = 15/50
= 3/10
Probability of drawing a black ball = 2/5 (given)
20/x = 2/5
x = 50 = no.of balls
Let no. of white balls be y
Now Probability of getting a white ball = 3/10 (given)
y/50 = 3/10
y = 15
Thus,No.of red balls = 50-(20+15)
= 50-35
= 15
Therefore, Probability of getting a red ball = 15/50
= 3/10
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