1. 40 tens regroup to tens
40 tens = 40 x 10, because it says 40 tens
so how many tens are there in 400
=> 400 divided by 10
=> 400 / 10
=> 40
Thus, we will regroup 40, by tens 4 times to get the answer
=> 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10
There are 40 10s in 40 tens
Thus the answer when we add this 40 tens is 400