= =%%..

啦啦啦

alcohol and water are mixed in the ratio of 4:1 in volume. if 15% of alcohol is evaporated,and

an additional 30% of the original amount of water is added ,

what is the ratio of alcoholl of water in the final mixture ?

要let 數,,點做=0= ..

abc666

let the total initial volume of mixture be 100cm3
final volume of alcohol
=80 X (1-15%)
=68cm3
final volume of water
=20X(1+30%)
=26cm3

final ratio of volume of alcohol to water
=68:26
=34:13

PS. I found that I can never remember how to spell 'alcohol'~.~

[ 本帖最後由 abc666 於 1/10/2007 03:06 PM 編輯 ]

Royal

Let the original volume of this mixture be X
--> the original volume of alcohol is 4/5 X
--> the original volume of water is 1/5 X

As 15% of alcohol is evaporated, there are only (100%-15%)(4/5 X) of alcohol remains.
Also, (1/5 X)(30%) of water is added, thus there is (1/5 X)(100%+30%) of water in the mixture.

  Alcohol remained
=(100%-15%)(4/5 X)
= 0.85 (4/5 X)
= 0.68 X

Water remained
= (100%+30%)(1/5 X)
= 1.3 (1/5X)
= 0.26 X

So, the ratio of alcohol of water
       = 0.68 X / 0.26 X
       = 34 / 13

如果你真係唔識solve呢類問題，你可以畫一d圖幫自己諗，
又或者好似abc666咁let一個實數去代。
(懇請大家唔好針對我d grammar xd= =)