A student has
English books and
history books. In how many ways can this student put the books on the shelf so that books of the same subject would stand together?
Five girls and five boys are sitting down on
chairs one after one. In how many ways they can sit so that boys would sit on the chairs with even numbers and girls - in the chairs with odd numbers?
In how many ways can the orders of printing
different books be distributed to
students in a classroom. Each second student exchanged a pen for another one. How many times pens were exchanged?
How many different six-digit numbers can be formed out of ? Digits should not repeat and only even digits should be at the beginning and the end of a number.
men working for security service. It is needed to organize protection of two buildings with three and four floors (one man on each floor). In how many ways it can be organized?
candies. In how many ways she can give these candies to her
children so that each gets
boys in the class. In how many ways four pairs for a school dance can be chosen out of them? (A pair means boy-girl pair)
The coin is being tossed by two times. What is the probability of tails coming up both times?
-card deck there are
cards in each. What is the probability when after dealing cards to four players (each gets nine cards), everyone gets cards of the same suit?