Write down three consecutive whole numbers just preceding $851001$.

$248+639=639+$_____

$6245+(631+751)=(631+$ _____ $)+751$

$1946+$ _____ $=387+1946$

Find the value of : $753+807+947$

Determine $1983+647+217+353$ by using suitable property.

Determine the following sum by suitable rearrangement.

$1+2+3+4+96+97+98+99$

Complete the following magic square by supplying the missing numbers.