請幫忙列式-急急

2) 15-(r-6) =6-(3r+5)15-r+6=6-3r-5
21-r=1-3r
2r=-20
r=-103) 5(c+1)-(c+8)-11 =0
5c+5-c-8-11=0
4c=14
c=14/4
c=7/2
4) x/2+x/3 =0
6(x/2+x/3)=0x6
3x+2x=0
5x=0
x=0


5) (y+2) /5= y/4
20[(y+2) /5]=20(y/4)
4y+8=5y
y=8


2010-07-27 16:15:14 補充：
LET x is the number of girls.
280(2)/7=50%x
80=x/2
x=160

2010-07-27 16:20:57 補充：
or,
LET x and y is the number of girls and boys respectively.
50%x=2y/7
x=4y/7

(7份2)(= 2/7)

Actually, which one is correct?
(2份7)(= 7/2) or (7份2)(= 2/7)

2010-07-29 22:34:35 補充：
Sorry, 比錯評價...