[xpi0t0s]

1.50
1.50
1.50
-----
4.50
-----
Now add 0.40

But how do you know that you have to add .40? Dividing by 100 doesn't simplify the problem, which is essentially all you've done.

2.00
1.25
1.25
===
4.50

So do we add .40 or not? Why?