中二數學~不懂怎計請幫幫手

4.)A chicken and a duck cost $45 ......1)
5 chickens and 6 ducks cost $250......2)
5chicken and 5 duck cost $225 .....3)
2)-3)1 DUCK=25
A chicken =45-25=20

2007-02-08 15:47:58 補充：
5)Three pens and two rubbers together cost $52 The cost of a rubber is two-thirds the cost of a pen 2/3PEN=1RUBBER Three pens and 4/3 PENS COST$52 4.1/3PENS=52 A PEN= $12 A RUBBER=2/3PEN =$8

2007-02-08 15:50:41 補充：
Two aticles cost $51 ONE OF THEM LESS $3THE HIGH PRICES is($51＋$3)/2＝$27 ANOTHER＝$27－$3　　　　　　　　　　　　　　　＝　＄２４

2007-02-08 15:56:41 補充：
７）ｉ　ｄｏｎｔ　ｕｎｄｅｒｓｔａｎｄ　ｗｈａｔ　ｙｏｕ　ａｓｋ

2007-02-08 16:09:41 補充：
７）One-sixth of the sum of two numbers is 3　　the sum of two numbers ＝１８　　and eight times their difference is 32（ｎｏｔ　ｓｕｒｅ）

2007-02-10 12:53:00 補充：
8a－8b＝32a＋b＝18．．．．１）　　ａ－ｂ＝４．．．２）ａ＝１８－ｂ　．．．３）ｔａｋｅ３）ｔｏ２）１８－ｂ－ｂ＝４１８－４＝２ｂ１４＝２ｂｂ＝７ａ　ｉｓ　１８－７＝１１ｔｈｅ　ｔｗｏ　ｎｕｍｂｅｒｓ　ｉｓ　７ａｎｄ１１　　

let $x be the price of chicken , $y be the price of duck
x+y=45...(1)
5x+6y=250...(2)
x=45-y...(3)
sub(3) into (2)
5(45-y)+6y=250
225-5y+6y=250
y=25
x=20


let $a be the cost of pen,$b be the cost of rubber
3a+2b=52...(1)
b=2/3a...(2)
sub(2)into(1)
3a+2(2/3a)=52
a=12
b=8

let $c be the cost of article1 ,$d be article2
c+d=51...(1)
c-3=d...(2)
sub(2)into(1)
c+c-3=51
c=27
d=24