how did you get 7/2 x 5/4, did u do this to get it:
3x2 =6+1=7 then use the same demominator= 7/2
1x4=4+1=5 then use the same demominator =5/4
and by 5/4 do u mean ??
Specifically, what he did was write 3 as 6/2 so that 3+ 1/2= 6/2 + 1/2= 7/2 and write 1 as 4/4 so that 1+ 1/4= 4/4+ 1/4= 5/4. And, yes, 5/4 is just a simpler way of writing
As to what you wrote, yes, 6+1= 7 but no, 3x2 is not equal to 6+ 1!