7号考试，急：请教官方模考中的两个数学

fly_holly

1. In the squence of  positive numbers x1,x2,x3... what is the value of x1?

(1)xj=x(j-1)/2  (2)x5=x4/(x4+1)

答案是C，我选择E

2. If the terms of a squence are t1 t2 t3...tn, what is the value of n?

(1) the sum of the n terms is 3124 (2) the average (arithmetic mean)of the n terms is 4.

程雅祺

Q1. 由（1）和（2）可以退出X4=1，然后利用（1）推出X1=8

Q2. sum/n=average (arithmetic mean)of the n terms

   （1）说了sum=3124，（2）说了average (arithmetic mean)of the n terms =4

n=3124/4=781  选C