To multiply  numbers having zeros at the end:      ex. 6000×1200

-Ignoring the ending zeros multiply together the rest of the digits. This yields the first part of the answer.    ex.  6×12=72_ _ _ _ _

-Count the ending zeros in the numbers being multiplied, and place that many at the end of the answer.      ex. _ _ 00000

 

Simple:     400×600=240000       222,200×30,000=6666000000