求教“最新13套题”试卷一的几道数学题

魏小妞要出国

Q7:
A certain university will select 1 of 7 candidates eligible to fill a position in the mathematics department and 2 of 10 candidates eligible to fill 2 identical positions in the computer science department.If none of the candidates is eligible for a position in both departments, how many different sets of 3 candidates are there to fill the 3 positions?


A.42
B.70
C.140
D.165
E.315为什么选E呢~？
Q10:
What is the value of (x - y)⁴?
(1)The product of x and y is 7.
(2)x and y are integers.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

我觉得应该选E，可是答案是C，请帮我解答一下~

Q13:
If n is a positive integer, what is the remainder when 3⁸ⁿ⁺³ + 2 is divided by 5?


A.0
B.1
C.2
D.3
E.4
最怕这种余数题，请NN帮帮~~
我是这样做的的，3^{8n+3    
尾数应该是9（4次一循环），那么9+2=1，那么余数应该是0呀，可以为什么答案是4呢~？}

Q25:
If the sequence x₁, x_2, x_{3, …,} x_n, … is such that x₁ = 3 and x_n+1= 2x_n – 1 for n ≥ 1, then x₂₀ – x₁₉ =


A.2¹⁹
B.2²⁰
C.2²¹
D.2²⁰ - 1
E.2²¹ - 1
不明白为什么答案选A

Queeny11

1 你可能题目没读明白  就是从7个人中抽一个区这个部门  从10个人中抽两个去另外一个部门 问有几种抽发  C(1,7)*C(2,10)
2 X Y相乘是7 并且都是整数的话  只能一个是1 一个是7 所以就求出来了
3  3的次方。多写几个发现 尾数只能是 3 9 7 1。。然后每四个循环
 8n+3对应的3的次方尾数只能是7  加2  也就是9 除以5 余数是四
4 xn+1= 2xn – 1
  xn+1——1=2（xn – 1） 成等比数列了。。看出来了吧。。。