Question

A bag contains white ,black and red balls only .A ball is drawn at random from the bag.If the probability of getting a white ball is 3/10 and that of a black ball is 2/5,then 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.

Answer 1

Answer:

Step-by-step explanation:

Solution :

Let the no of white balls be = x

Let the no of red balls be = y

number of balls black balls =20

total number of balls =x+y+20

Probability of getting a white ball =3/10

xx+y+20=310

=> 10x=3x+3y+60

=> 7x−3y=60------(1)

Probability of getting a blind ball =25

(i.e)20x+y+20=25

= 100=2x+2y+40

=> 2x+2y=60

or x=y=30 ----------(2)

Solving (1) and (2) we get,

7x−3y=60

x+y=30

______________

7x−3y=60

7x+7y=210

________________

−10y=150

=> y=15

x=15

Answer : 15

Answer 2

Probability of getting a white ball = 3 / 10

Probability of getting a black ball = 2 / 5

Total number of black balls = 20

Let the Probability of getting a red ball be x.

Then, x + 3 / 10 + 2 /5 = 1

x = 1 - [ ( 3 + 4 ) / 10]

x = ( 10 - 7) / 10

x = 3 / 10

Number of black balls = 20

Probability of getting a black ball = 2 / 5

20 / T = 2/5

T = 50 [ T = Total outcomes ]

$<h4>Total number of balls in the bag = 50$