Front end estimation involves rounding off a number to the leftmost place and using that in the addition problem. With front end estimation, 43 + 52 becomes 40 + 50; 43 is rounded down to 40, and 52 is rounded down to 50, only adding the leftmost numbers.
No matter how many digits are in the number, with front end estimation, only the number in the leftmost position remains after rounding up or down. All other numbers are turned into zeros. For example, if 4,222 is used in a front end estimation problem, it becomes 4,000 before it is added or subtracted in the equation.