2 math questions

Stella

I doubt the answers of these 2 questions are right, so could you guys take a look, thanks!

1. It's 6:00pm, and Amy has to stay in office until laura calls her.  After each hour Amy is in the office, there's a 70% chance that Laura will call her.  What's the probability that Amy will not be able to leave the office until 9:00pm?
a..027 b.063 c. .09  d. .147   e. .343, the answer is b, but I think it's a

2.what's the volumne of a room with length x feet, width y feet, and height z feet?
(1) x= 1200/yz
(2) the area of the ceiling is 120 square feet, and the area of each of the 2 facing walls is 100 square feet.
the answer is a, but I think it's d.

brigittew

2. we can get the exact result throught the term 1, by xyz=1200/yz*yz=1200
through term 2, we get xy=120, yz=100, thus xyz=xy*(100/y)=100x, however, we cant get exact result of x throught the given condition
so i think the correct answer should be A

Stella

Thanks, twinhead.  I think so as well.  What's more important should be the process of thinking, so let's just pass this question. 3 Q,

tongxun

yes，cook。

cook

2. I thought the question 2 should tell us that the room is a rectangle, not irregular , isn't it?

twinhead

the area of each of the 2 facing walls is 100 square feet
这句话应解释为:
1 两个面对的墙的面积每个都是100
还是:2 每两个面对的墙的面积都是100

也就是应该理解成"和"还是"或"存有理解上的疑义
字面上each是修饰两个面对的墙的,表示pair1或pair2的相对墙面积100
如果理解为和的含义如解释中tell us the area of xy, yz, and xz
不用解只要乘起来就得xyz!怎么不能得出呢?ft压
所以一来PR的表述有歧义或错误,二来解释肯定错
个人认为

Stella

Thanks to you mater guys.  But I still have questions about no. 2.  There's explaination for no. 2.  It says you can't know xyz from xy=120, yz=100, and xz=100.  It means statement 2 tell us the area of xy, yz, and xz.  Why can't we solve the 3 equations? Actually, I've got the number of x,y, z.  So, what's going on?  PS. it's not JJ, it's from PR.

twinhead

2正如tongxun所解释的
方程组:
(1)xy=a
(2)yz=b或xz=b
不能确定xyz的值

twinhead

1 not until表示直到...才
I will not A until B happen.表示B发生是A发生的充分条件,只有B发生才能有A发生
所以Amy has to stay in office until laura calls her的意思为:
Amy没有接到laura的电话就必须呆在家里,即
Amy has not to leave office until laura calls her
直到接到laura的电话才能离开
而Amy will not be able to leave the office until 9:00pm
表示Amy直到9点才能离开
所以自然是0.3*0.3*0.7=0.063
老兄大概是把这句话堪称直到9点仍未离开了
BTW:此题如此细微的语言表达且如此精确,应该不是jj吧?

tongxun

2. Form the condition (2), we know that xy=120, and yz=100, but xyz=? we cannot get it. I think the facing wall may mean the wall having no door inside it.