Depends. All multiples of 400, you could have many different options. For example, 400 buses 1 kid on ea. 40 buses 10 kids on ea.
400x1=400
40x10=400
Just if the two numbers multiple to 400 it can be an answer
164+219=383 is exact for estimate round 164 to 165 or 160 and 219 to 220 so
165+220=385 or 160+220=380
