+9673 Look at the last 3 digits of the bigger number.(Of course 4875837 is bigger......)
Add the last 3 digits of 4875837(i.e. 837) to the smaller number(i.e. 45), which result is 882.
Put the remaining 4 digits of the bigger number to the result.
Answer: 4875882.
That's my way of quick calculations :D
If you have a enormously large number and a 3 digit number adding together then look at the last 4 digits of the bigger number and repeat what I did.
