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题目内容
The units digit of $$7^{n}$$ is r, and the units digit of $$9^{n}$$ is t, where n, r, and t are positive integers. Which of the following could be the value of r+t?

Indicate all such values.
How many integers between 100 and 1,000 are multiples of 7?
Z=$$123^{4}$$-$$123^{3}$$+$$123^{2}$$-123

What is the remainder when Z is divided by 122?
$$n$$ is a positive integer.

Quantity A

$$\frac{1}{3^{n}}$$

Quantity B

$$3(\frac{1}{4^{n}})$$


How many positive divisors of 210 can be expressed as a product of two prime factors?
xy ≠ 0 , x > y

Quantity A

$$\frac{1}{x}$$

Quantity B

$$\frac{1}{y}$$


a ≠ 0

Quantity A

a+1

Quantity B

$$\frac{1}{a}$$ - 1




-1 < x < 1

Quantity A

|1-x|

Quantity B

1


Quantity A

The number of positive even integers less than 100, each of which is the square of an integer

Quantity B

The number of positive odd integers less than 100, each of which is the square of an integer


There are two parallel lines, and the third line intersects these two lines.

Quantity A

The number of points with equal distance from three lines

Quantity B

3


Two sides of an isosceles triangle have lengths 5 and 5.

Quantity A

The perimeter of the triangle

Quantity B

15


Eight students of different heights need to be arranged into two rows of seats. Each row has four seats. For each column, the student in the row ahead needs to be shorter than the student in the row behind. In how many ways can these students be arranged?
An urn contains 4 red balls, 8 green balls and 2 yellow balls. Five balls are randomly selected WITH replacement from the urn. What is the probability that 1 red ball, 2 green balls, and 2 yellow balls will be selected?

Give your answer as a fraction.
An eight-digit integer is formed by three "1" and five "2". How many different such integers can be formed?
Event A and event B are independent event. If the probability that even A occurs is 0.4 and event B occurs is 0.3, what will be the probability that at least one event occurs?

Give your answer as a decimal.


In an equilateral triangle ABC,three points P,Q and R are on the side AB,AC and BC, respectively.

Quantity A

The sum of any two interior angles in Δ ABC

Quantity B

The sum of any two interior angles in Δ PQR




Quantity A

a

Quantity B

b




Quantity A

x

Quantity B

90




△ABC is an isosceles triangle, BA=BC, DE is parallel to AC. If the perimeter of both triangle BDE and quadrilateral ADEC equals to 18 (the length of all the sides are integers), then what is the length of DE?

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