$A$ card is selected from a pack of $52$ cards. Calculate the probability that the card is an ace of spades.

Consider the experiment in which a coin is tossed repeatedly until a head comes up. Describe the sample space.

Events $A, B$ and $C$ are mutually exclusive events such that $P(A)=\frac{3x+1}{3}$,$P(B)=\frac{1-x}{4}$ and $P(C)=\frac{1-2x}{2}$. The set of possible values of $x$ is in the interval

Boxes $B_1, B_2$,and $B_3$ contain balls as given below:

Box	White	Black
$B_1$	$1$	$2$
$B_2$	$3$	$1$
$B_3$	$2$	$3$

One ball is drawn at random from each box. Then,among the balls drawn,the probability that two are black and one is white,is

Three randomly chosen non-negative integers $x, y$ and $z$ are found to satisfy the equation $x+y+z=10$. Then the probability that $z$ is even,is

An experiment consists of rolling a die and then tossing a coin if the number on the die is even. If the number on the die is odd,the coin is tossed twice. Write the sample space for this experiment.