F.2 maths

Q: The numbers of marbles owned by Alex and Brian are in the ratio

3 : 2. If Alex gives 80 marbles to Brian, the marbles owned by Brian

will be four times as many as that owned by Alex. Suppose Alex has

x marbles while Brian has y marbles originally

(a) Set up two equations with unknowns x and y

(b)Find the values of x and y

Sol:

( a )

Suppose Alex has x marbles while Brian has y marbles originally,

then

x : y ＝ 3 : 2

2x ＝ 3y

2x － 3y ＝ 0 ....... equation ( 1 )

4 ( x － 80 ) ＝ y ＋ 80

4x － 320 ＝ y ＋ 80

4x － y ＝ 400 ....... equation ( 2 )

( b )

( 2 ) － ( 1 ) × 2

5y ＝ 400

y ＝ 80

2x － 3 × 80 ＝ 0

2x － 240 ＝ 0

x ＝ 120

Ans: ( a ) as shown as above ( b ) x ＝ 120, y ＝ 80

你好呀..f.2 仔 ^^ 做法同上面有 d唔同
佢跳左好多步

( a )

x : y ＝ 3 : 2
x/y = 3/2

2x ＝ 3y........( 1 )

4 ( x － 80 ) ＝ y ＋ 80

4x － 320 ＝ y ＋ 80

4x － 240 ＝ y ....... ( 2 )

( b )

Sub 4x － 240 ＝ y to (1) ,
2x = 3( 4x － 240 )
12x = 720
x = 60
Sub x = 60 to (1),
2(60) =3y
y = 40

so x=60 and y = 40


加油~

2008-01-02 17:26:08 補充：
原來我打錯野.. 唔好意思我好俾心機咁改返..xd( a )x : y ＝ 3 : 2x/y = 3/22x ＝ 3y........( 1 )4 ( x － 80 ) ＝ y ＋ 804x － 320 ＝ y ＋ 804x － 400 ＝ y ....... ( 2 )

2008-01-02 17:26:28 補充：
( b )Sub 4x － 240 ＝ y to (1) , 2x = 3( 4x － 400 )2x = 12x-1200x = 120Sub x =120 to (1), 2(120) =3yy = 800so x=120 and y =80