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

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

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

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

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