Question

a bag has 20 black balls and some black balls. When 10 more white balls are added, the probability of drawing black balls becomes 3/4th of the probability of drawing black balls find orignal white balls in the bag.
​

Answer 1

Step-by-step explanation:

Bag I= 3 White + 7 Red + 15 Black

Bag II= 10 White + 6 Red + 9 Black

Each beg contains total of 25 balls.

There are three cases for selection of a particular ball :

1. White ball from Bag I and Bag II=

25

3

×

25

10

2. Red ball from Bag I and Bag II=

25

7

×

25

6

3. Black ball from Bag I and Bag II=

25

15

×

25

9

∴ Total probability =

625

30

+

625

42

+

25

135

=

625

207

.

Hence, the answer is

625

207

.