有几道数学题想请教下大家~~

xyxyxy_123

1.For any integer n greater than 1, n
denotes the product of all the integers
from 1 to n, inclusive. How many
prime numbers are there between
6 + 2 and 6 + 6, inclusive?
(A) None
(B) One
(C) Two
(D) Three
(E) Four  这道为什么选的是a？
2. If an integer n is divisible by both 6 and
8, then it must also be divisible by
which of the following?
(A) 10
(B) 12
(C) 14
(D) 16
(E) 18  这道16为什么不可以？答案是12
3. Of the science books in a certain
supply room, 50 are on botany, 65 are
on zoology, 90 are on physics. 50 are
on geology, and 110 are on chemistry.
If science books are removed
randomly from the supply room, how
many must be removed to ensure that
80 of the books removed are on the
same science?
(A) 81
(B) 159
(C) 166
(D) 285
(E) 324 这道能给详细的解题步骤嘛？ 答案是E
4.A certain shade of gray paint is
obtained by mixing 3 parts of white
paint with 5 parts of black paint. If 2
gallons of the mixture is needed and
the individual colors can be purchased
only in one-gallon or half- gallon cans,
what is the least amount of paint, in
gallons, that must be purchased in
order to measure out the portions
needed for the mixture?
(A) 2
(B)2又1/2
(C) 3
(D)3又1/2
(E) 4  这道答案是B还是E啊？

xyxyxy_123

xyxyxy_123

xyxyxy_123

xyxyxy_123

温润的风

第一个没看懂
第二个24不行 6是23 8只有2  n要包括23

温润的风

第三个就是不让它拿够80 先拿五六十的怎样都不会超过80 然后总数超过的品种拿79 直到不能再多拿一本

xyxyxy_123

温润的风 发表于 2016-3-20 20:47
第一个没看懂
第二个24不行 6是23 8只有2  n要包括23

那个不是14 嘛？24？ 2和4？

xyxyxy_123

温润的风 发表于 2016-3-20 20:50
第三个就是不让它拿够80 先拿五六十的怎样都不会超过80 然后总数超过的品种拿79 直到不能再多拿一本 ...

哦~ 明白了 谢谢~

温润的风

温润的风 发表于 2016-3-20 20:50
第三个就是不让它拿够80 先拿五六十的怎样都不会超过80 然后总数超过的品种拿79 直到不能再多拿一本 ...

24能除以16么 为啥不行 因为16里面没有3这个元素 但是n里面有 因为6里面有