There are white balls and black balls in the bag , from which you can pick any two at a time.

　　(1) Find the probability that the two balls obtained are of different colors.
　　(2) Find the probability that one of the two balls obtained is black.

out of keys can open the door. Now take keys and find the probability that they can open the door.

Two letters are randomly put into mailboxes. Find the probability that there is no letter in the first mailboxes and the probability that there is only one letter in the first mailbox.

There are playing cards in a deck . Sampling without replacement, one card at a time, consecutive cards, find the probability that the four cards have different suits.

There is one red, one yellow, one black ball each in the bag, and three draws are made with one replaced. Find the probability of the following events:

three times all the balls are red , 

three times no black balls are drawn ,

The colors are all different , 

The colors are not all the same .

Randomly select different numbers from and try to find the probability of the following events:

The three numbers do not contain and ;

The three numbers do not contain or .

Pick any cards (without repetition) from a deck of playing cards , and calculate the probability that at least of the cards taken out have the same suit.

There is a couple among people. They sit randomly around a round table. Find the probability that the couple happens to sit together.

Among the products, there are defective products and genuine products, of which are chosen at random .
　　(1) Find the probability that there are exactly defective products;
　　(2) Find the probability that there are at least defective products.

Choose any pairs of shoes from different pairs . What is the probability that at least two of these shoes will match each other?

rivets are randomly taken and used on parts. Among them, rivets are too weak. Use rivets for each part. If all rivets with too weak strength are installed on one part, then this part The strength is too weak. What is the probability that a component is too weak?

During the reexamination of a graduate student in a certain major, there are test tickets and candidates take the test. One person draws one and immediately puts it back. Then another person draws, and the people draw once each. What is the probability that at least one test ticket has not been drawn after the drawing is completed?

Randomly pick times with replacement from integers from to , pick a number each time, and find the probability that the product of the numbers taken is divisible by .

A and B agree to take a bus at a certain station between pm and pm. There are buses during this period , and their driving times are , , , and respectively . If they agree to wait for one car at most, find the probability that A and B ride in the same car. Assume that the arrival times of A and B at the station are not related to each other, and it is equally possible for each person to arrive at the station at any time from o'clock to o'clock.