怎樣可以清楚寫出step?

Let y m^2 be the original size of the farm
% change={[y(1-20%)](1+30%)-y}/y x100%
=[0.8y(1.3)-y]/y x100%
=(1.04y-y)/y x100%
=y(1.04-1)/y x100% 抽common factor y出黎,之後約左佢
=0.04x100%
=4%

p.s. 唔洗solve個y出黎,,,因為你既目的係計% change
呢個已經係full step!
要清楚寫出step,,,係要先let左佢,,,呢個step一冇就即扣,,,因為人地都唔知y係咩黎
跟住寫番 新減舊除舊x100% 條式出黎,,,人地就會知你計緊咩(最好寫埋% change就萬冇一失)
solve左之後就ok架啦!

2007-01-03 14:06:25 補充：
唔記得左仲有個重要既step,,,冇佢就死記得寫conclution呀!!!4% was increased in the total yield of the farm.(正既就increase,,,負既就decrease,,,咁樣會清楚d)

[(1 - 20%)(1 + 30%) - 1] x 100%
= (0.8 x 1.3 - 1) 100%
= (1.04 - 1) x 100%
= 4% (increased)