有題數學題......急!!!!!!!!!!!!幫幫忙!!!

假設這個數字的十位數是x; 個位數是y

x = y+3 .... (1)
5(x+y) = 10y+x+7 ==> 5x+5y = x+10y+7 ==> 4x = 5y+7 ==> x = (5y+7)/4... (2)

(1) = (2)
y+3 = (5y+7)/4
4y+12 = 5y+7
4y+5 = 5y
y = 5

From (1),
x = 5+3 = 8

所以, 原數是85

2007-11-20 22:04:27 補充：
當然啦, 好似樓上, 原數 = 8x10+5 = 85另外, 你想check 條數有無計錯, 可以如下check清楚:十位數字比個位數字大3 ==> 8-5 = 3 (無錯)數字之和的5倍較數字次序倒換後所成的新數大7==> (8+5) x 5 - 7= 58 (無錯)

2007-11-24 22:08:39 補充：
甲乙兩數之比為5:4，乙丙兩數之比為2:3==> 所以, 甲:乙:丙 = 5:4:6換句話說, 甲=5k; 乙=4k; 丙=6k (k 是常數)1/3 (5k+6k) = 4k + 1.... (1)11k = 12k + 3k = -3甲 = 5 * (-3) = -15 (* 是乘號)乙 = 4 * (-3) = -12丙 = 5 * (-3) = -18

2007-11-24 22:08:54 補充：
check下有無計錯, 在(1) 依條式內:左邊 = 1/3 [(-15)+(-18)] = 1/3[-33] = -11右邊 = -12 + 1 = -11==> 無計錯

設原數十位為x,個位為y,

則原數為10x+y

x-y=3-----------------------(1)

5(x+y)-(10y+x)=7------(2)

從(1),x=y+3--------------(3)

代(3)入(2),

5(y+3+y)-(10y+y+3)=7

12-y=7

y=5

代y=5入(3),x=5+3=8

所以原數是10(8)+5=85