F1 mathematics-要快(要步驟)

Let the number of $2 coins is y, then the no. of $1 coins is 3y & $5 coins is y-5
The equation :

3y+2y+5(y-5)=325
3y+2y+5y-25=325
10y-25=325
10y=325+25
10y=350
y=35
She has 35 $2 coins

let the no. of $2 coins be X,no. of $1 coins be 3X,no. of $5 coins be (X-5)

2X+3X+5(X-5)=325
2X+3X+5X-25=325
10X=350
X=35

so she have 35 $2 coins

let the number of $2 coins be a
3a+5(a-5)+2a=325
5a+5a-5=325
10a-5+5=325+5
10a/10=330/10
a=33

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2007-10-16 19:50:56 補充：
o sor拆括號時miss 左x5添let the number of $2 coins be a3a 5(a-5) 2a=3255a 5a-25=32510a-25 25=325 2510a/10=350/10a=35

let x,y and z be the number of $1 conis, $2coins and $5coins respectively
x=3y
y-5=z
x+2y+5z=325
3y+2y+5(y-5)=325
5y+5y-25=325
10y=350
y=35
She has 35 $2coins

Let Donna has x $1 coins

So, she has x/3 $2 coins

she has (x/3 - 5) $5 coins


Total value = 325

i.e. x + 2(x/3) + 5(x/3 - 5) = 325


x + 2x/3 + 5x/3 - 25 = 325

10x/3 = 350

x = 105

So, she has 105/3 = 35 $2 coins