# cancellation problem in float-point numbers

In http://en.wikipedia.org/wiki/Floating_point#Addition_and_subtraction, it gives an example about cancellation problem in float-point numbers, see

I don't understand why it is written :

The best representation of this difference is e = -1; s=4.877000, which differs more than 20%.....

In this example, it uses IEEE 754 decimal32 format.

Could someone explain the idea about cancellation problem in float-point numbers as this example want to illustrate?