中四數學問題

Let a be the total volume of cocktail
Let b be the volume of alcohol inside the cocktail

8% of alcohol inside the cocktail
a x 8% = b.............................. equation (1)

6% of cocohol inside the cocktail if 50ml of fruit juices was added
(a + 50 ) x 6% =b.................... equation (2)

equation (1) - (2)
=> (a x 8%) - (a + 50) x 6% = b-b
(a x 8/100) - (a x 6/100) - (50 x 6/100) = 0
a x 2/100 = 300/100
a x 2 =300
a = 150

So the total volume of the said cocktail is 150 ml, then the volume of alcohol inside the said cocktail is

by using equation (1)

a x 8% = b
150 x 8/100 = b
So b = 12

Therefore, there have 12ml of alcohol inside the cocktail.

B: 12ml

設原有x毫升酒精,
共有雞尾酒:
x/8%=12.5x(毫升)
加果汁後有雞尾酒 12.5x+50(毫升)
所以這時有酒精:(12.5x+50)*6%=(0.75x+3)(毫升)
即
0.75x+3=x
3=x-0.75x
0.25x=3
x=12
答案係D:12mL

2007-07-26 12:08:58 補充：
值得注意的是,加果汁前後酒精的量是相同的另外,答案係B唔係D,我攪錯左對唔住