數學題.XD...8D...

設家成有X元，志偉有Y元，康健有Z元
X - Y = 9 ---------- (1)
Z = 1/3 X ---------- (2)
X + Y + Z = 61 ---------- (3)
由(1), Y = X - 9 ---------- (4)
張(2)及(4)代入(3),
X + (X - 9) + 1/3 X = 61
7/3 X - 9 = 61
7/3 X = 70
X = 30
張X = 30代入(4), Y = 30 - 9 = 21
張X = 30代入(2), Z = 1/3 (30) = 10
所以家成有30元，志偉有21元，康健有10元

Let x be the amount of money of 志偉
Then, 家成 has x+9
And 康健 has (x+9)/3
x + x+9 + (x+9)/3 = 61
x + x+9 + (1/3)x+3 = 61
(7/3)x +12 = 61
(7/3)x = 49
7x = 147
x = 21
Therefore, 志偉 has $21,
家成 has $30
And 康健 has $10
Sum of the amount of their money = $61
Therefore the answers are correct. - -

志偉 = x
家成 = x+9
康健 = (x+9)/3

x+x+9+(x+9)/3=61
2x+9+(x+9)/3=61
(6x+27+x+9)/3=61
7x+36=183
7x=147
x=21