The probability of an impossible event,i.e.,$P(\phi)$,is:

An anti-aircraft gun can take a maximum of $4$ shots at an enemy plane moving away from it. The probabilities of hitting the plane at the first,second,third,and fourth shots are $0.4, 0.3, 0.2,$ and $0.1,$ respectively. What is the probability that the gun hits the plane?

$A$ bag contains $2$ red,$3$ green and $2$ blue balls. Two balls are drawn at random. What is the probability that none of the balls drawn is blue?

In a simultaneous toss of $2$ coins,find the probability of getting no tail.

In a class,$30 \%$ of students passed English,$20 \%$ passed French and $10 \%$ passed both. If a student is selected at random,what is the probability that he has passed English or French?

The probability that a contractor will get a plumbing contract is $2/3$ and the probability that he will not get an electric contract is $5/9$. If the probability of getting at least $1$ contract is $4/5$,what is the probability that he will get both?