Question

a bag contains 10 playing cards . 7 of which are Black and 3 Red . Two cards are drawn one after the other from the bag without replacement. A. Find the probability that a Red and a Black cards were drawn. ​

Answer 1

I think it should be done by using tree diagram so here it is

Answer 2

Number of red balls =3

Number of black balls =7

Total number of balls =10

Let ,P(A)= Probability that first is red

P(B)= Probability that second is red

If second is red, there are 2 possible ways

Either first is red and second is red.

Or first is black and second is red.

So,

P(B)=

10

3

C

1

×

9

2

C

1

+

10

7

C

1

×

9

3

C

1

=

90

6

+

90

21

=

90

27

=

10

3

Probability that first is red, given second is red

P(A/B)=

P(B)

P(A∩B)

=

10

3

10

3

C

1

×

9

2

C

1

=

10

3

90

6

=

90

6

×

3

10

=

27

6

=

9

2