For an event,the odds against are $6 : 5$. The probability that the event does not occur 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 $P(A) = \frac{1}{2}$,$P(B) = \frac{1}{3}$,and $P(A \cap B) = \frac{1}{4}$,then find the value of $P(A' \cap B')$.

If $A$ and $B$ are two independent events,then the probability of occurrence of at least one of $A$ and $B$ is given by $1 - P(A') P(B')$. Is this statement true or false?

In class $XI$ of a school,$40\%$ of the students study Mathematics and $30\%$ study Biology. $10\%$ of the class study both Mathematics and Biology. If a student is selected at random from the class,find the probability that they will be studying Mathematics or Biology.