數方程[十二月十三日九點前答]

let 像皮擦 be x,pen be y,

{ 3y+x=34 ...(1)
{ y+5x=26 ...(2)

y+5x=26
y=26-5x...(3)

(3) into (1)
3(26-5x)+x=34
78-15x+x=34
14x=78-34
14x=44
x=3.1

y+5(3.1)=26
y+15.5=26
y=10.5

'.'像皮擦 is $3.1and the pen is $10.5

Let $x be the amount of 1 pen.
Let $y be the amount of 1 rubber.
3x+y=34........1
{
x+5y=26........2
3x+y=34
3x=34-y
x=(34-y)/3

x+5y=26
(34-y)/3+5y=26
(34-y)/3=26-5y
34-y=3(26-5y)
34-y=78-15y
34-78=-15+y
-44=-14y
14y=44
7y=22
y=22/7
y=3+1/7

3x+y=34
3x+22/7=34
3x=34-22/7
3x=30+6/7
x=10+2/7
∴The amount of a rubber is $3.1(cor. to 1 dp.).

Let a and b be the price of a pen and a rubber respectively

Thus,
{3a+b=34-------(1)
{a+5b=26-------(2)

(2) become
a=26-5b-----(3)

Put (3) into (1)
3(26-5b)+b=34
78-15b+b=34
-14b=34-78
-14b=-44
b=3.14 (corr. to 3 sig.fig.)

Put b=3.14 into (2)
a+5(3.14)=26
a+15.7=26
a=26-15.7
a=10.3

∴The price of a rubber is $10.3

2007-12-13 18:20:25 補充：
respectively = 分別地

2007-12-14 18:27:42 補充：
用一倏式計唔到,根本冇得用一條式