Question 760488
If we toss 2 coins simultaneously, the possible outcomes are as follows.
(where H = heads, T = tails)

If Coin1 shows Heads and Coin2 shows Heads, let us represent it as (H,H)

If Coin1 shows Heads and Coin2 shows Tails, let us represent it as (H,T)

Thus, we have the following combinations:
(H,H) (T,T), (H,T), (T,H) - exactly 4 possible results.


From the above, you can see that exactly 2 of the 4 outcomes have "exactly one head" i.e. (H,T) and (T,H)


As you know, probability is defined as 
{{{Number of favourable outcomes / Total number of possible outcomes }}}

In this case, getting "exactly one head" is the favourable outcome.

Hence the probability of getting exactly one head is {{{ 2 / 4 = 0.5 }}}