Question

Two unbiased coins are tossed simultaneously. Find the probability of getting

(i) two heads (ii) at least one head (iii) at most one head.

Answer 1

If two unbiased coins are tossed simultaneously, we obtain any one of the following as an out come :

HH, HT, TH, TT

So,  Total number of elementary events = 4

(i) Two heads are obtained if elementary event HH occurs.

So,  Favorable number of events = 1

Hence, P (Two heads) =1/4

(ii) At least one head is obtained if any one of the following elementary events happen: HH, HT, TH

So,  favorable number of events = 3

Hence P (At least one head) =4/6=2/3

(iii) If one of the elementary events HT, TH, TT occurs, than at most one head is obtained

So,  favorable number of events = 3 

Hence, P (At most one head) =3/6=1/2