中一數學問題

設 有 a個1元及b個5亳硬幣
a+b = 130--------------(1)
a($1)+b($0.5) =$ 107----(2)
由方程式(1), 得出: b= 130-a,
套入方程式(2), 得出:
a + (130-a)(0.5) = 107
a + (65 - 0.5a) = 107
0.5a = 107 - 65
0.5a = 42
a= 84
b = 130 - a
= 130 -84
= 46
袋中有1元硬幣 84個 5毫硬幣46個

設X=1元 , Y=5毫
X + y = 130..........(1)
X + 0.5y = 107..........(2)
(1) X = 130-Y 代入 (2)
130-Y+0.5Y = 107
130-107 = 0.5Y
Y = 46
Y = 46 代入 (1)
X = 130-46 = 84
笞案 : 1元有84個, 5毫有46個

let x be the no, of $1 coins and y be the no. of 50cents coins.

x + y = 130 .....(1)
x + 0.5y = 107.....(2)

From (1), x = 130 -y ....(3)

Substitute (3) to (2),
130 - y + 0.5y = 107
23 = 0.5 y
y = 46 .....(4)

Substitute (4) to (3),
x = 130 - y
x = 130 - 46 = 84

so
no. of $1 coins is 84
no. of 50 cents coins is 46