比﹕比例(例步驟)。‧；

I only know No. 3:
已知 x 和 y 是非零的數, 而(x+y): (y+3)=5 : 3。求x : y
In the question, there is a term, (y+3), consist of a constant,
and I cannot deal with ratio, so, there is no solution.




2012-01-30 16:36:28 補充：
No. 5:
已知一個盒子裹五角 、二角和一角這三種硬幣數目的比是3 : 2 : 1。
若盒中所有硬幣的總值是20元, 求五角硬幣的數目。
:)
3a(0.5) + 2a(0.2) + 1a(0.1) = 20
1.5a + 0.4a + 0.1a = 20
2a = 20
a =10
:)
the number of 0.5 coin
= 3a
= 3 x 10
= 30

2012-01-30 16:43:05 補充：
No.4.:
若x : y=5 : 3 , 求 2x-y / (除號)x+3y 的值。
:)
as x : y=5 : 3
then y = 3x / 5
:)
2x-y / (除號)x+3y
= 2x - 3x/5 / x + 3(3x/5)
= 10x/5 - 3x/5 / 5x/5 +9x/5
= 7x/5 / 14x/5
= 7x / 14x
= 1/2
done
:)

2012-01-30 16:51:34 補充：
No.1:
已知3x=4y=7z，求x : y : z
:)
x : y : z = (4x7) : (3x7) : (3x4)
x : y : z = 28 : 21 : 12
:)
done
:)

2012-01-30 16:56:24 補充：
No.2:
若 x : y : z= 28 : 21 : 12 及y+z-x=10, 求x,y,z的值
:)
y + z - x = 10
21a + 12a - 28a = 10
5a =10
a = 2
:)
x = 28a
x = 56
:)
y = 21a
y = 42
:)
z = 12a
z = 24
:)
done
:)