Maths problems!!!!!!!!!!!!!!!!

Here is my answer.

1.A. I only

It's because if the ratio of a,b and c is 3:2:1. We can say that a is 3x, b is 2x and c is x. We can use this to calculate the three situations.It's always correct.

In the situationI. a/3= b/2= 1, we can operate it like this:

3x/3=2x/2=1

In the situation II and III, we should remember that it may be correct but not must. It's because as we know before, a=3x , b=2x and c=x, x can be any number. If it is 1, then the two situations will be correct. But in fact, in other situations when x is not equal to one, it will not be correct.

2a. From the question, we know that the volume of the new mixture is 2V. and it has (7+3+x+y) parts.

So the volume of alcohol in the new mixture is:

2V* (x+7)/(7+3+x+y)

= 2V(x+7)/(10+x+y)

b. According to 2a, the volume of water in the new mixture is:

2V* (y+3)/(7+3+x+y)

= 2V(y+3)/(10+x+y)

第一題MC……冇個岩……=0=

2009-01-04 21:35:57 補充：
首先，如果 a:b:c=3:2:1
咁應該有 a=3k, b=2k, c=k

於是有 a/3 = b/2 = c/1 = k
但(I)只有 a/3 = b/2 = 1，所以唔岩。
如果岩既話，就有 a=3, b=2，但唔可以確定。

至於如果 k=1，咁(I), (II)同(III)都岩，
但因為冇講明 k=1，所以都唔可以肯定。

(I), (II), (III) 三個都係may be correct，
但冇一個係must be correct。

2009-01-04 22:00:14 補充：
好簡單，如果取 a=6, b=4, c=2
咁就有 a:b:c = 3:2:1，但三個都唔岩。