According to the question, three coins are tossed together.

By using the formula of probability, we get,

P (E) = favourable outcomes / total possible outcomes

Total number of possible outcomes is $2^3=8$

Let E be the event of getting at least one head and one tail

E = {(H, T, T) (T, H, T) (T, T, H) (H, H, T) (H, T, H) (T, H, H)}

n (E) = 6

P (E) = n (E) / n (S)

= 6 / 8

= 3/4