there are seven pies if i take away 2 1.3 how many are left
Is that 2 1/3? If so, you start out with 7 * 3/3 = 21/3 pies,
You take away 2 1/3 = 7/3 pies,
leaving (21-7)/3 = 14/3 = 4 2/3 pies
Or, you could consider 7 pies as 6 + 3/3 pies
Take away 2 + 1/3
leaving 4 + 2/3
Treat units and "thirds" as separate quantities, which cannot be lumped together.