AP EAMCET Engineering 21 Apr 2019 Shift 2 Paper

Consider A and B be the events when the sum is obtained as 7 and 11 respectively.
Number of times sum 7 and 11 occurs,
n(A)={(2,5),(5,2),(3,4),(4,3),(1,1),(6,1)}=6
n(B)={(5,6),(6,5)}=2
Now, the probability is,
P(A)=‌

6

36

=‌

1

6

P(B)=‌

2

36

=‌

1

18

The probability when neither the sum of 7 or 11 occurs,
P(C)=‌

36−(6+2)

36

=‌

7

9

The probability that 7 comes before 11
P‌‌=‌

1

6

+‌

1

6

×‌

7

9

+(‌

7

9

)2(‌

1

6

)+(‌

7

9

)3(‌

1

6

)⋅....
‌‌=‌

1

6

(‌

1

1− 7 9

)
‌‌=‌

3

4