Because what your doing is breaking apart the dividend to make it easy to divide with the divisor. Example 189/3 What you do is place value in hundreds would be 180/3= 60 9/3=3 add together you get 63
If 48 students remain on the bus and 23 had been dropped off, all we have to do is add 48 + 23 and then you'll get the answer as of how many kids were in the beginning.
