寫出方程(列式)

let 5蚊=x,,2蚊=y,,5蚊數量=a,,2蚊數量=b

ax + by = 25. ......(1
a + b = 8 ......(2
--------------------------------------↑重點
--------------------------------------↓解釋
因為ax=5a
by=2b
5a + 2b = 25 ......(3
a = 8 - b ......(4

sub 4 to 3
5 ( 8 - b ) + 2b =25
40 - 5b + 2b - 25 = 0
15 - 3b = 0
15 = 3b
b = 5

sub b = 5 to (4)
a = 8 - 5
a = 3

所以 5蚊數量 = 3 ,, 2蚊數量 = 5
呢個先係你最想要既答案xDD

Put x, y be the number $2 and $5 coins x+y=8=- 2x+5y=8 solving equations, x=5 and y=3.
∴There are 5 $2 coins

If number of $5 is x
number of $2 is y
x+y=8 i
5x+2y=25 ii
x=3 y=5
The number of $2 is 5

Let x and y be the number of $2 and $5 coins respectively.
x+y=8=----1
2x+5y=25----2
By solving these equations, x=5 and y=3.
∴There are 5 $2 coins.

$5is 3,$2is 5
let be $2is 5,
$2x5+$5x3=25=8(coins)

2012-08-15 13:59:10 補充：
Why everyone answer is same?