just can't figure it out...:(

lisaislisa

from XDF GMATCAT [em15]
1. three-digit number , if the first digit is a prime number and the last number is also a prime number , how many numbers accord with the pattern ?
AN 160

[em15][em15][em15][em15][em15][em15][em15]

2 the formula for diagnals and sides for polygon is d=n(n-3)
if the diagnals is twice as many as the sides , what side there will be
An is 7
but mine An is 5
as 2n=d ,d=n(n-3) => n=5
I failed to find out the flaws from my An ,although I am afraid it's just a easy pro....[em17]

THaNKs to All [em19]
[em19]

lisaislisa

yeah , you guys just hit the tail of the nail...;)

it's so glad to meet  all of you and find we're just pursuing the same target
we are blessed the brilliant future !
as long as we exert utmost ^^

GRD from Lisa in SH

freedim

exposition bidding  呵呵是“申博”吧  

BATI巴蒂：  you are welcome！ 办的这么好的一个网站，这么多人风雨同舟的奋斗，我当然也要勉力尽上自己的力量，其实跟大家讨论，我也收获很大的！

BATI巴蒂

LISA, "exposition bidding" 是指什么. 不管怎样看你高兴,我也为你高兴.

FREEDIM,  非常感谢你在这段日子帮助我们回复和解答网友们的帖子.  
代表所有斑竹感谢你.也祝你在骄傲的日子里会有着动人的笑容.

lisaislisa

so 1 is not prime number ?...
humble quesiton , isn't it ...
anyway , just got the news of succeed in exposition bidding ..
so excited !!!
grant all of you good luck ^^

BATI巴蒂

1. 10以内的质数只有4个:2,3,5,7.
则有: 4*10*4=160

2. 答案为5.

freedim

QUE1:   0-9中质数2，3，5，7  所以C4^1*C10^1*C4^1=160

QUE2;   I agree with yours