[求助 PREP -2 - MATH

ben168

aa) if K <> 0, 1, or -1,  is 1/k > 0?

1)  1/ (k-1)  >0

2)  1/ (k+1) > 0

标准答案是a)

可是我搞不懂为什么？

bb) what is the value of positive integer m?

1)  When m is divided by 6, the remainder is 3

2) when 15 is divided by m, the remainer is 6

应该是两者结合都无法得出结论。可是答案是 b)

谢谢!

[此贴子已经被作者于2009-1-5 1:13:23编辑过]

ben168

还有两题：

cc) at a certain store, each notepad costs x dollars and each marker costs y dollars. if $10 is enough to buy 5 notepads and 3 markers, is $10 enough to buy 4 notepads and 4 markers?

1) Each notepad costs less than $1

2) $10 is enough to buy 11 notepads

答案是E)

dd) a certain basket contains 10 apples, 7 red, 3 green.  if 3 different apples are to be selected at random frombasket, what is the probability  that 2 red and 1 green?

不好意思，一直都做不好这种题。答案是21/40

ben168

ding yi xia

emma227

以下是引用ben168在2009-1-5 1:15:00的发言：

还有两题：

cc) at a certain store, each notepad costs x dollars and each marker costs y dollars. if $10 is enough to buy 5 notepads and 3 markers, is $10 enough to buy 4 notepads and 4 markers?

1) Each notepad costs less than $1

2) $10 is enough to buy 11 notepads

答案是E)

enough 和equal不一样，没有个定值，所以算不出来

dd) a certain basket contains 10 apples, 7 red, 3 green.  if 3 different apples are to be selected at random frombasket, what is the probability  that 2 red and 1 green?

不好意思，一直都做不好这种题。答案是21/40

分母，从10ge里面选3个组合，C10，3，分子，从7个红苹果选2个C7，2，从3个绿苹果选1个，C3，1，因为是分步计算中的两个步骤，所以相乘作为分子

specman

aa)

1) 1/(k-1)>0 ==> k>1 ==> 1/k >0;
2) 1/(k+1)>0 ==> k>-1 不能推出1/k >0;

bb)
2)15被m除6， m为>6的整数 且15 = m * x + 6 ==> m = 9