Front end estimation
With front end estimation, we
only round and add the numbers in the leftmost place or the very last number on the left.
This means that all numbers in other places will be zeros except the number in the leftmost place after the numbers are rounded
Having said that, if the numbers have
two digits,
round to the tens place before adding the leftmost digits or numbers
Examples:
67 + 43 can be approximated by 70 + 40 = 110 Note that we are only adding the leftmost numbers (7 and 4)
21 + 58 can be approximated by 20 + 60 = 80
67 − 42 can be approximated by 70 − 40 = 30
98 − 32 can be approximated by 100 − 30 = 70
If the numbers have
three digits, round to the nearest hundred place before adding the leftmost digits or numbers
Examples
164 + 690 can be approximated by 200 + 700 = 900
Note that with front end estimation, all other numbers except the leftmost digits (2 and 7) are equal to zero and we only added the leftmost digits as stated before
235 + 455 can be approximated by 200 + 500 = 700
566 − 254 can be approximated by 600 − 300 = 300
722 − 568 can be approximated by 700 − 600 = 100
If the numbers have
four digits, round to the nearest thousand place before adding the leftmost digits or numbers
Examples
2354 + 1677 can be approximated by 2000 + 2000 = 4000
Note that all other numbers except the leftmost digits (2 and 2) are equal to zero and we only added the leftmost digits as stated before
5687 − 2765 can be approximated by 6000 − 3000 = 3000
3245 + 1897 can be approximated by 3000 + 2000 = 5000
7501 − 4508 can be approximated by 8000 − 5000 = 3000
If the numbers have
five digits, round to the nearest ten thousand place before adding the leftmost digits or numbers
Examples
48974 − 25799 can be approximated by 50000 − 30000 = 20000
Note that all other numbers except the leftmost digits (5 and 3) are equal to zero and we only subtracted the leftmost digits as stated before
82113 + 37893 can be approximated by 80000 + 40000 = 120000