#### 题目列表

In a list, the n-th term$a_{n}=2+a_{n-1}$ when n is even, while $a_{n}=-8+a_{n-1}$ when n is odd. If $a_{1}=6$, then what is the value of $a_{7}$?
If $a_{1}=1$, $a_{n}=a_{n-1}+n$, what is the value of $a_{49}$?
If $a_{1}=1$,$a_{n}=2a_{n-1}+r$,where r is a positive number. if $a_{1}+a_{2}+a_{3}=35$,what is the value of r?
List A: 1,-2,3,-4,5,-6-
In the list above, the absolute value of every number is 1 greater than the absolute value of the former number, in positive and negative in turn. What is the sum of the first 99 numbers?
For any positive integer n, $a_{n}= \frac{1}{n+1}- \frac{1}{n+3}$

#### Quantity A

The sum of the first 10 terms

#### Quantity B

$\frac{3}{4}$

$a_{1}=2$,$a_{2}=3$,当n≥3时,$a_{n} = a_{n-1} * a_{n-2}$.What is the value of $a_{8}$?
S={1,2,3}
T={1,2,3,4}
Quantity A: The number of different four-digit integers formed by elements from Set S(all elements can be used by more than once)
Quantity B: The number of different three-digit integers formed by elements from Set T(all elements can be used by more than once)
There are three different frames and five different pictures. Now choose three pictures to put into frames, one for each frame, how many possible ways to put them.
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?
In how many different ways can 5 identical small balls be placed in 3 different baskets so that each basket must have at least one small ball?
A, B, C, D and E need to take seats such that A and B sit next to each other. How many ways can they arrange the seats?
Four different books A, B, C, D are to be placed on the shelf, A and B must be put together. How many different ways can the four books be placed?
Four different toys need to be put into three different kids. At least one toy should be given to each kid. In how many ways can these toys be arranged?
The 8 items A, B, C, D, E, F, G, and H are to be displayed on a straight line. In how many ways can the items be displayed if item B must be placed in any position that is to the right of item A,and item C must be placed in any position that is to the right of B?
In a box of 10 electrical parts, 2 are defective. If someone selects 2 electrical parts randomly, what is the probability that neither of the parts will be defective?
How many positive divisors of 16 are multiples of 3?
If someone selects two numbers from 5,8,9,9,9 without replacement, what is the probability that the sum of the two numbers is multiple of 3?
There are 12 bags of spice, which includes 5 different flavors. Among these, one bag`s flavor is C and 5 bags is of cherry flavor. What is the probability that one C flavor and one cherry flavor are drawn out when someone draw two bags of spice from the 12 bags?