UPSC NDA II 2015 Mathematics Solved Paper

Let P denote the probability of getting head in a single toss of a coin.
∴p=

1

2

⇒q=

1

2

Let X denote the no. of heads in 5 tosses of a coin. then, X is a binomial variate with parameters; n=5 & p=

1

2

∴Req. probability=P(x>3)
=1−P(x≤3)
=1−[5C0+5C1+5C2+5C3]‌‌

1

25

=1−[1+5+10+10]‌‌

1

32

=‌‌

32

32

−‌‌

26

32

=‌‌

6

32

=‌‌

3

16