There are $n$ letters and $n$ addressed envelopes. The probability that all the letters are not kept in the right envelope,is

There are $3$ urns $A, B$,and $C$. Urn $A$ contains $4$ red balls and $3$ black balls. Urn $B$ contains $5$ red balls and $4$ black balls. Urn $C$ contains $4$ red balls and $4$ black balls. One ball is drawn from each of these urns. What is the probability that the $3$ balls drawn consist of $2$ red balls and $1$ black ball?

$A$ card is drawn from a pack of $52$ cards. If $A =$ card is of diamond,$B =$ card is an ace and $A \cap B =$ card is the ace of diamond,then events $A$ and $B$ are

$A$ box contains $10$ mangoes,out of which $4$ are rotten. $2$ mangoes are taken out together. If one of them is found to be good,the probability that the other is also good is

Six boys and six girls sit in a row randomly. What is the probability that the six girls sit together?

$A$ box contains $4$ red balls,$5$ green balls and $6$ white balls. $A$ ball is drawn at random from the box. What is the probability that the ball drawn is either red or green?