方程...... 急用(要題解~唔該)

上面個位仁兄，你d數好似錯左bo~睇清楚d啦~
註:第1-6條的「/」是除號，但第7條的「/」是分數符號，非除號!
1)
Let N be the boys:
N+N-6=40
N+N=46
2N/2=46/2
N=23
The boys are 23.
40-23=17
The grils are 17.
2)
Let N be the elder sister:
N+5+N-2+5=32
N+N+5+5-2=32
2N+8=32
2N+8-8=32-8
2N/2=24/2
N=12
The elder sister's age is 12.
12-2=10
The smaller sister's age is 10.
3)
Let N be he/she bought the number of books.
5*3+2N=19
15+2N=19
2N/2=4/2
N=2
He/She bought 2 books.
4)
Let N be the cattle's weight:
N+200+N+N-100=550
3N=450
3N/3=450/3
N=150
The cattle's weight is 150 kg.
5)
(4a-5b)(4a+8b)
=4a(4a+8b)-5b(4a+8b)
=16(a^2)+32ab-20ab-40(b^2)
=-24(a^2)+12ab
6)
好無奈(2x-y)(3x「=」2y)
無啦啦多左個「=」
先唔理住~goto 7)
7)
3/4[1+1/2(-2+1)]
=3/4[1+1/2(-1)]
=3/4[1+(-1/2)]
=3/4(1/2)
=3/8
8)
[-21+10(5-29-1+3)]/11
=[-11(-22)]/11
=242/11
=22
9)
5{21+7[-5-2(-4+3)]}
=5{21+7[-5-2(-1)]}
=5[21+7(-2)]
=5[21+(-14)]
=5(7)
=35
好喇~返回第6條(唔想計，唉...)
if "=" = "+" (睇唔睇得明?)
(2x-y)(3x+2y)
=2x(3x+2y)-y(3x+2y)
=6(x^2)+4xy-3xy-2(y^2)
=6(x^2)+xy-2(y^2)
else if "=" = "-" //(寫得太多理d野，慣左，唔好怪我- -)
(2x-y)(3x-2y)
=2x(3x-2y)-y(3x-2y)
=6(x^2)-4xy-3xy+6(y^2)
=6(x^2)-7xy+6(y^2)

註釋:
如1(x^2)
1是和x^2連著的，但因為^2不影響1這個數
所以我把它們分開!

2008-03-08 22:48:32 補充：
上面果個人第4條錯運算過程
5,6,錯寫法
唔應該xxx=0
而第5條佢將答案「約簡」，我唔肯定個做法岩唔岩，我要返去問下teacher，之後我會補充~
錯誤:
1.由於yahoo將「'」變左'
請自行變回!
2.句子if "=" = "+" (睇唔睇得明?)同句子else if "=" = "-" //(寫得太多理d野，慣左，唔好怪我- -)都唔駛理，因為yahoo顯示唔到~好騮! !
if...果句係話如果係+
else if...果句係話如果係-

仲有，一至四條我用左d唔太好的英文，希望你睇得明- -

2008-03-13 17:58:42 補充：
我搵到喇~
係可以約或唔約簡都ok~
sorry~girl我都串錯- -
好蠢- -