请教prep1数学题

１）what is the greatest common divisor of positive integers m and n?

(1) m is a prime number.

(2)2n=7m

why choose C?　

２）A certain law firm consists of 4 senior partners and 6 junior partners. How many different groups of 3 partners can be formed in which at least one member of the group is a senior partners? ( two grops are considered different if at least one group member is different. )

Why is 100?

３）If the operation $ is one of the four arithmetic operations addition, subtraction, multiplication, and division, is (6$2)$4=6 $(2$4)?

(1) 3$2 >3

(2) 3$1=3

Why choose A?

４）Is Z equal to the median of the three positive integers X,Y, and Z?

(1) X<Y+Z

(2) Y=Z

Why choose B?

1.问m,n的最大公约数。1）单独不成立。 条件2）由于nm都为整数，m不能取奇数；当m=2，n=7 最小公约数是1；当m=4，n=14 最小公约数为2...当条件1，2一起，则m=2。

2.C(1,4)*C(2,6)+C(2,4)*C(1,6)+C(3,4)

3.1)$可以是乘号或加号，代入原式成立。2）$可以是乘号或除号，除号时不成立。

4.1)不能确定xyz的大小，无法按顺序排列，则无法确定中数。2）当y=z，x大于或小于y和z，三个数按序排后，y或z是中数。