For two events $A$ and $B$,if $P(A \cup B) = 5/6$,$P(A^c) = 5/6$,and $P(B) = 2/3$,then $A$ and $B$ are

If the odds against solving a question by three students are $2:1$,$5:2$,and $5:3$ respectively,then the probability that the question is solved by only one student is

If $A$ and $B$ are mutually exclusive events,given that $P(A)=\frac{3}{5}$ and $P(B)=\frac{1}{5}$,then $P(A \text{ or } B)$ is

If a number is selected from the first $30$ natural numbers,then the probability that the number selected is divisible by $4$ or $7$ is:

If the probabilities of a student passing in the first,second,or third grade are $1/10$,$3/5$,and $1/4$ respectively,then the probability of the student failing (getting a fourth grade) is ........

If $A$ and $B$ are any two events,then $P(A \cup B) = \dots$