#### 题目列表

A four-digit integer is formed out of 0, 1, 2 and 3 (the same number could be used by more than once) where the sum of all the digits is 3. How many integers in total meet the requirement?
How many factors of 210 can be expressed as the product of two prime numbers?
How many points (r, s) can be formed so that r < s, and that the x and y-coordinates of the point are both selected from odd integers between 1 and 399, inclusive?
Four guests A, B, C and D have to be assigned into three different rooms (one double room and two single rooms) such that A and B wont have to stay in the double room at the same time. How many ways in total can they be assigned into these rooms?
Linda has 4 jackets, 3 pants and 2 pairs of shoes. She could choose 1 jacket, 1 pant and 1 pair of shoes every day. However, 1 jacket and 1 pant dont match, so they cannot be selected together. In such circumstance, for how many days can she wears differently?
In how many ways can 4 kids (2 boys and 2 girls) be selected out of 5 couples of boy-girl twins such that no kids are selected from the same couple?
What is the probability that the one 3-digit and one 2-digit integers that could be formed out of 1, 2, 3, 4 and 5 (each figure is used for only once) are both even integers?
Eight points are equally spaced on a circle. If 4 of the 8 points are to be chosen at random, what is the probability that a quadrilateral having the 4 points chosen as vertices will be a square?
If points A and B are randomly placed on the circumference of a circle with radius 2, what is the probability that the length of chord AB is greater than 2?
In a box of 5 red socks, 4 blue socks and 3 yellow socks, someone selects a sock first, puts it back and then selects another sock. What is the probability that he or she selects yellow socks for both time?
What is the probability of selecting different colors when selecting 2 balls out of a box of 10 red balls and 6 blue balls without replacement?