第一次做GMAT，数学错了几个 求解 谢谢各位

zhanshi2012

1.     For every positive even integer n, the function h(n) is defined tobe the product of all the even integers from 2 to n, inclusive. If p is thesmallest prime factor of h(100)+1, then p is
(a) BTW 2 to 10
(b) BTW 10 to 20
(c)  BTW 20 to 30
(d) BTW 30 to 40
(e) Greater than 40
2.     If r and s are integers and rs+r is odd, which of the followingmust be even?
(a) r
(b) s
(c)  r+s
(d) rs-r
(e) r^2+s
3.     An investment of d dollars at k simple annual interest rate yields$600 interest over a 2-year period. In terms of d, what dollar amount investedat the same interest rate will yield $2400 interest over a 3-year period?
(a) 2d/3
(b) 3d/4
(c)  4d/3
(d) 3d/2
(e) 8d/3
4.     A basket contains 5 apples, of which 1 is spoiled and the rest aregood. If Henry is to select 2 apples from the basket simultaneously and atrandom, what is the probability that the 2 apples selected will include the spoiledapple?
(a) 1/5
(b) 3/10
(c)  2/5
(d) 1/2
(e) 3/5

lingdang123

第1题，呼唤大神…………

第2题，rs+r=r*(s+1)=奇数，所以r和（s+1)都是奇数，所以s是偶数。r+s=奇数+偶数=奇数，rs-r=r*(s-1)=奇数*奇数=奇数，r^2+s=奇数+偶数=奇数

第3题，因为说了是单利计息（simple annual interest rate)，所以有：d*k*2=600,解得k=300/d。设要求的investment of dollars=x，则有x*k*3=2400,即x*300/d=800，所以x=8d/3

第4题，随机选2个苹果包含spoiled的概率是：第一个是spoiled，第二个是good=1/5*1;第一个是good，第二个是spoiled=4/5*1/4=1/5。两种情况相加得2/5

bloodlust

h(100)=2*4*6*8*10.....*100
         =(2*1)*(2*2)*(2*3)*(2*4).....*(2*50)
         =2^50*(1*2*3*4*5*.........50)
h(100)+1=2^50*(1*2*3*4*5*.........50)+1

所以1到50都不可能整除h（100）+1
所以应该选e