10. 25000 square yard的场地, 摆放5000个crate, 问每个crate 的最大占地面积是多少square feet? (45 s feet)
25000/5000 * 3^2
17. 有三种车, fullsize, midsize, compact, 这三种车中有31辆白车, 19辆兰车, 10辆红车, 问白色fullsize的车有多少?
a. 兰车和红车都没有fullsize的车
b. b. fullsize 的车比midsize和compact总和还多. (C )
a = > (19+10)<fullsize <31 => 29<fullsize <=31 => 29 <=midsize + compact < 31
b => fullsize > midsize + compact
a+ b =>fullsize = 31, midsize + compact = 29
19. 一群学生, 每个人有 3 pen+1pencil , 或有 1pen+2pencil, 平均每个学生拥有1.6支pen, 问拥有pencil的平均数? ( 1.8)
(3x + y) / (x+y )= 1.6
(x+ 2y) /(x+y) = 1.8
21. r, s, t. 是连续整数, 问3^r + 3^s + 3^t 的最大质因子? (13 )
r = n-1 s = n, t= n+1
3^r + 3^s + 3^t = 3^(n-1)* 13
so, the maximum of its prime fators is 13
28 20克碳原子有6.02x10^23个碳原子, 问1.806x10^24重多少克? (120克)why ?my answer:60
20 : 6.02 = X : 18.04
明天就要考了,急问几题,谢谢大家
[此贴子已经被作者于2004-12-13 22:55:59编辑过] |