Question

There are n balls in a drawer, of which 7 are red. If 2 balls are chosen randomly, then the probability that both
are red is 3/4. Find n.​

Answer 1

Step-by-step explanation:

4- Green 5- Blue 3- Red

(i) Red in colour → total = 4+5+3=12

⇒

12

3

=

4

1

(ii) not Green in colour:- means balls maybe blue or Red.

Blue + Red = 5+3=8 and total = 12

So : Answer is

12

8

=

3

2

Answer 2

Answer:

8

Step-by-step explanation:

Total number of balls = n

Total number of red balls = 7

Probability of randomly drawing a red ball = 7/n

Probability of randomly drawing a red ball after drawing the first red ball = (remaining red balls)/(remaining balls) = 6/n-1

Probability of both red balls = 3/4

Probability of drawing a red ball after drawing a red ball = (7/n) (6/(n-1)

(7/n) (6/(n-1)) = 3/4 => n = 8