There need not be any estimated digit but, if there must be one, then it is the last digit: 3.
.0002 is the estimated number
170
4082 Since the tens digit is 2 times the thousand digit, it must be an even digit. So it can be 8, 6, 4, or 2. But, the thousands digit is 4 greater than the hundred digit. So that the hundred digit must be 0, the thousands digit must be 4, the hundreds digit must be 8, and the ones digit must be 2.
the leading digit
The answer depends on the extent to which the number is being estimated.
the estimated digit in 0.0782m is?
There need no be any estimated digit.
3750 and 4250
The last digit is always the estimated digit in a number
There need not be any estimated digit but, if there must be one, then it is the last digit: 3.
500
There need not be any estimated digit: there could well be exactly 4500.
It is always the last digit.
.0002 is the estimated number
It is 0.08 M
It is the zero at the end.