！比和率！！比和率！！比和率！！比和率！！比和率！

Q1:若x:z=5:2和y:z=4:9，求x:y。
x : z = 5 : 2
z : y = 9 : 4
x : z : y = 45 :18 : 8
so x:y=45:8

Q2:若X:Z=7:2和Y:Z=3:5，求y:z。
X : Z = 7 : 2
Z : Y = 5 : 3
X : Z : Y = 35:10:6
I think there must be some mistake in the question
but you can find the ratio from the result I find

Q3:3a=2b和4b=5c，求a:b:c
3a=2b
so a:b = 2:3
4b=5c
so b:c = 5:4
a : b = 2 : 3
b : c = 5 : 4
a : b : c = 10:15:12

Q4:3a=4d:=5c，求a:b:c
First I think the question should be 3a=4b=5c
3a=4b
we get a:b = 4:3
4b=5c
we get b:c = 5:4

a : b = 4 : 3
b : c = 5 : 4
a : b : c = 20:15:12