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

$A$ positive integer is selected at random and is divided by $9$. What is the probability that the remainder is equal to $1$ (in $/9$)?

If two balanced dice are tossed once,the probability of the event,that the sum of the integers coming on the upper sides of the two dice is $9$,is

From a pack of $52$ cards,$4$ cards are drawn. What is the probability that it has two digit-cards and one honours card of black suit and one honours card of red suit?

Two dice are thrown. Find the probability of getting an even number as the sum.

In an entrance test,there are multiple-choice questions. There are four possible answers to each question,of which one is correct. The probability that a student knows the answer to a question is $90\%$. If he gets the correct answer to a question,then the probability that he was guessing is: