Use front-end rounding to estimate the sum

Explanation

We will use front-end rounding to approximate each addend. Then we  will find the sum of the approximations. Front-end rounding produces addends containing many 0’s.Such numbers are easier to add. Each of the addends is rounded to its largest place value so that all but its first digit is zero. Then we add the approximations using vertical form.

3,714   →    4,000  (round to the nearest thousand)
2,489   →    2,000  (round to the nearest thousand)
   781   →       800 (round to the nearest hundred)
5,500   →    6,000  (round to the nearest thousand)
+ 303   →   +  300 (round to the nearest hundred)
12,787       13,100

Note the estimate is very close from the actual sum.  It is just 313 more than 12,787.  The calculation is easier to perform and they take less time, but the answers are not exact.