Question

a ball contains 40 balls pu of which some are red and others are blue remaining black.if the probability of drawing red ball is 11/20 and that of blue ball is 1/5 then what is no of black ball
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Answer 1

Answer:

no of balls =40

probability of red =11/20=>11/20 *2/2 =>22/40

(as total no of balls is 40 converting dinominator to 40)

like wise,

probability of blue = 1/5 => 1/5 *8/8 =>8/40

let probability of black balls be x/40, no of black balls is x

probability of getting any ball = 40/40

•°• 40/40 = probability of red+ probability of blue + probability of black

= 22/40 +8/40 +x/40

= 30/40 +x/40

= 30/40+x/40

=>30+x=40

=>x=40-30

=>x= 10

Hence no of black balls equals to 10