F.1 MATHS, {ratio] 急急急!!! 趕住溫習!!!

1. a+2:a+5:b=3:4:7
(a+2)/(a+5)=3/4
4a+8=3a+15
a=7
a+2/b=3/7
9/b=3/7
b=21
2. a:b=7:5
c:d=5x3/10:5x7/10
c:d=3/2:7/2
a:c:d=7:3/2:7/2=14:3:7
3. 4:(x+3)=3:(2x-1)
4(2x-1)=3(x+3)
8x-4=3x+9
x=13/5

2008-03-29 15:56:58 補充：
002 的第三題是錯的.

F.1 MATHS, {ratio] 急急急!!! 趕住溫習!!!


1.Given that (a+2):(a+5:b=3:4:7.Find the values of a and b.

(a+2) : a+5 = 3:4 ==> 4(a+2) = 3(a+5) == >4a+8 = 3a+15
==> a = 7
(a+5) : b = 4 : 7 == > (7+5) : b = 4:7
==> b = 21


2.A brithday cake is divided into ywo parts A and B in the ratio 7:5.
The smaller part is further dovided into tw parts C and D in the ratio 3:7.
Find the ratio of areas of A:C:D

7:5 , in 5 == > 3:7
7:5 >> 14:10
Find the ratio of areas of A:C:D
==>> 14:3:7


3.If 4:(x+3)=3:(2x-1),Find x.
==> 3(x+3) = 4(2x-1)
==> 3x+9 = 8x-1
==> 5x = 10
==> x = 2

要清楚列式,,所有steps!!!
thz a l0t!!!