Question

Explain how to find 40×50 using mental math

Answer 1

Just do 4x5 then add the zeros

Answer 2

Think about 40 over 50 and a line separating the answer from the problem like this:

                 40
              x 50
              ---------
                200         0*0=0 5*4= 20 so just put the zero back on the answer and you get 200.

the answer goes under the dotted line