TT_GWD_25-11,6

I searched the old discussions, but I haven't found the relative one.

Q11

Of the three-digit positive integers that have no digits equal

to zero, how many have two digits that are equal to each

other and the remaining digit different from the other two?

A.     24

B.     36

C.     72

D.     144

E.      216 (E)

Q6

A string of 10 lightbulbs is wired in such a way that if

any individual lightbulb fails, the entire string fails. If for

each individual lightbulb the probability of failing during

time period T id 0.06, what is the probability that the

string of lightbulbs will fail during time period T?

   A.0.06

   B.(0.06)^10

   C.1-(0.06)^10

   D.(0.94)^10

   E.1-(0.94)^10(E)

Q11, I guess the answer is E, but I got C91*c91*3=243, but there are some numbers repeated, so they have to be subtracted, but I don' t know why.

And Q6, I thought is (0.06)^10

Can sb. help? I will have my test in 7 days.

It's so bad, my computer cannot write in Chinese.

Q6

串联的灯泡任何一个的故障都会导致整串的failure,所以只要排除全部都完好的情况就是可能出现故障的概率了.

所以 1-(1-0.6)^10

Q11

如果相同的数字是1,另外的数字有8种可能

这两个1跟另外一个数字随机排列,有3种可能,那么一共有3*8种可能

想同的数字可以是1到9,9  种可能

那么一共就是9*3*8=216种可能