Explain how to find 40 x 50 using mental math

4*5 is 20. 
20 x 100 is 2000.
40 x 50 equals 2000.

I'm sorry if this is not the answer you were looking for but hopefully, I could help. 

Hello!

To solve 40 × 50 using mental math, you can use an easier way to solve it.

Take the first digits f the numbers (4) and (5).

Multiply those:

4 × 5 = 20

Now, ypu need to add the 0s from 40 and 50 to this number.

2000

You add the amount of 0s the numbers have to the new number, and that's your answer!