|
11. Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank. Working together at their respective constant rates, the pumps can fill the tank in 6 hours. How many hours will it take the small pump to fill the tank working alone?
答案应该是9小时。 16. A three-digit code consists of digits from 0 to 9. If the first digit cannot be 0 or 1, the second digit must be 0 or 1, and the second and third digits cannot be 0 at the same time, how many codes are possible?
该题目分为两种情况：
1、第二位是1：C81*C101
2、第二位是0：C81*C91
所以答案为：C81*C101+C81*C91=152种，注意原文给出的条件and the second and third digits cannot be 0 at the same time
18. What is the remainder when positive integer x is divided by 71). X+1 is divisible by 7 2). X+13 is divisible by 7
1) x+1=7a, x=7a-1,余数为6
2）x+13=7a, x=7a-13=7(a-2)+1, 余数为1
所以答案为D 20. K=wxyz, where w, x, y, z are prime numbers. Not including 1 and K, how many factors does K have? 总个数：c41+c42+c43=14个 补充一道： Q. In which quadrants do the roots of the equation lie, given x and y are integers: Y = (x-2)^2 -1 Y = (x-2)^2 -1 Y=x^2+4-4x-1 Y=x^2-4x+3 Y=(x-1)(x-3)
这道题目是一条抛物线，开口向上，在X轴截距是1和3，画图可知，该图形不能出现在第三象限.
1). X+1 is divisible by 7 2). X+13 is divisible by 7
1) x+1=7a, x=7a-1,余数为6
2）x+13=7a, x=7a-13=7(a-2)+1, 余数为1
所以答案为D 20. K=wxyz, where w, x, y, z are prime numbers. Not including 1 and K, how many factors does K have? 总个数：c41+c42+c43=14个 补充一道： Q. In which quadrants do the roots of the equation lie, given x and y are integers: Y = (x-2)^2 -1 Y = (x-2)^2 -1 Y=x^2+4-4x-1 Y=x^2-4x+3 Y=(x-1)(x-3)
这道题目是一条抛物线，开口向上，在X轴截距是1和3，画图可知，该图形不能出现在第三象限.
| 
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2006-10-8 10:41:00
