What is the mass attitude of elements in substances the formula which SO3?

given:
SO3
find:
m (S): m (O)
Solution:
Mr(SO3) = Ar(S)+ 3Ar(O) = 32  + 3 • 16 = 80
ω(S)=Аr(S)/Мr(SО₃)   = 32/80  = 0,4
ω(O)=3Аr(O)/Мr(SО₃)   = (3 • 16)/80  = 48/80= 0,6
m(S): m(О)=0,4/0,4 ∶ 0,6/0,4  =1∶1,5 = 2∶3
Answer: m(S) : m(О) = 2 : 3.