Suppose Page size=5 words,
then Frame 1 contains 0 To 4 words
similary, Frame 2 contains 5 To 9
So if you want to fInd physical address of words in Frame 3=(3-1)5+offset
ex.frame 3 contains =(3-1)5+0=10,
=(3-1)5+1=11,
=(3-1)5+2=12,
=(3-1)5+3=13,
=(3-1)5+4=14,
i.e.(Frame no-1)pagesize +offset
hence (fno-1)ps+offset is correct.