BITSAT 2016 Paper

As 0.4+0.6=1, the man either takes a step forward or a step backward. Let a step forward be a success and a step backward be a failure.
Then, the probability of success in one stepp=0.4=

2

5

The probability of failure in one step=q=0.6=

3

5

In 11 steps he will be one step away from the starting point if the numbers of successes and failures differ by 1.
So, the number of successes=6
The number of failures=5
or the number of successes =5
The number of failures =6
∴ the required probability =11C6p6q5+11C5p5q6