A bag contains white, red and black balls. A ball is drawn at random from the bag. The probability of getting a white ball is 3/ 10 and that of black ball is 2/ 5 . (a) Find the probability of getting a red ball. (b) If the bag contains 20 black balls, then find the total number of balls.
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let W be the white balls
let R be the red balls
let B be the black balls
P(W) + P(B)+ P(R) = 1 (the sum of all probablities is 1)
3/10 + 2/5 + P(R) =1
15+20/50 +P(R)=1
35/50 +P(R) =1
P(R)= 1- 7/10
P(R)= 3/10
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