Question

5. A bag contains 4 white balls and some red balls.If the probability of drawing a White
ball from the bag is 2/5 , find the number
of red balls in the bag​

Answer 1

Solution :

A bag contains 4 white balls and some red balls .

Let us assume that the number of red balls present in the bag is x.

The total number of balls present in the bag becomes ( x + 6) . This is the sample space .

Now, the probability of drawing a white ball :

> [ Number of favorable events ]/[ Total number of events ]

> [ 4 ]/[ x + 6]

But, the probability of drawing a white ball is 2/5 .

So,

4/(x+6) = 2/5

> 2(x+5) = 20

> 2x + 10 = 20

> 2x = 10

> x = 5.

Thus, there are 5 red balls in the bag,

This is the required answer.

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Answer 2

Question :-

A bag contains 4 white balls and some red balls if the probability of of drawing a white ball from the bag is $\frac{2}{5}$ Find the number of red balls in the bag.

Solution :-

Given Number of white balls $$=4

Let Number of red balls =N

then total balls =N+4

Probability of drawing a white ball from the bag would be

P (whiteball) = $\frac{No. of White Balls}{Total Balls}$ = $\frac{n(White)}{n(Total)}$ = $\frac{4}{n + 4}$

But Given P (whiteball) = $\frac{2}{5}$

So P(white Balls) = $\frac{2}{5}$ = $\frac{4}{n + 4}$

$\frac{2}{5}$ = $\frac{4}{n + 4}$

2(N + 4) = 5 ∗ 4

2N + 8 = 20

2N = 20 - 8 = 12

N = 6

So the number of red balls in the bag is 6 red balls.