The probability of happening an event A in one trial is 0.4. The probability that the event A happens at least once in three independent trials is

0.936 0.784 0.904 0.216

0.784

Here $P(A) = 0.4 $ and $P(\overline{A})=0.6$ Probability that A does not happen at all = $(0.6)^3$ . Thus required probability =$1 -(0.6)^3 = 0.784.$