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Front end estimationWith 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
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