F.1 maths 唔該><`

14.
Ben's age=14+4=18
Ben's age + Andy's age + Carl's age =52
Carl's age=52-14-18
=20
ratio of Ben's age to Carl's age=18:20=9:10
20.
a-2b=0
a=2b
3a=6b

3b=4c
6b=8c

3a=6b=8c
a:b:c=3:6:8

21.
1/a:1/b=3:4
1/a*ab:1/b*ab=3:4
b:a=3:4
b:a=15:20

1/b:1/c=6:5
1/b*bc:1/c*bc=6:5
c:b=6:5
c:b=18:15

a:b:c=20:15:18

14. The total age of Andy, Ben and Carl is 52. Andy is 14 years old, and Ben is
4 years older than Andy. What is the ratio of Ben's age to Carl's age?
ben's age : 14+4=18
carl's age :52-14-18=20
ben's age : carl's age = 18:20 =9:10

20. If a - 2b = 0 and 3b = 4c, find the ratio a:b:c.
a-2b=0
a=2b
a:b=2:1 = 8:4
3b=4c
b:c= 4:3
a:b:c=8:4:3

21. if 1/a:1/b=3:4 and 1/b:1/c=6:5,find the ratio of a:b:c
1/a:1/b=3:4
1
-------------
a 　　　　　　　　　　3
--------------- =---------------
1 　　　　　　　　　　4
-----------
b
b/a=3/4
4b=3a
b:a=3:4
a:b=4:3 =20:15
1/b:1/c=6:5
1
-------------
b 　　6
--------------- = ---------------
1 　　　　　　　　　　5
-----------
c
c/b=6/5
5c=6b
c:b=6:5
b:c=5:6 =15:18

a:b:c=20:15:18