Fundamental principle of probability theory

The probability that neither of the faces show an even number is 1/2 *1/2 =1/4. Hence the probability at least one is even is 1-1/4 = 0.75.

The probability that he misses the target all four times is given by $$0.4 ^ 4$$. Hence, the probability that he has hit the target is $$1 - 0.4 ^4$$ = 0.9744.

The probability of getting 0 heads is $$\frac{1}{32}$$.
The probability of getting exactly one head = $$ ^5 C _1 (0.5)(0.5^4) = \frac{5}{32}$$ and two heads = $$ ^5 C _2 *(0.5^2)(0.5^3)= \frac{10}{32}$$.

Hence probability of getting 3 or more heads = $$1-\frac{1}{32}-\frac{5}{32}-\frac{10}{32} = \frac{1}{2}$$