There need not be any estimated digit: there could well be exactly 4500.
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To estimate the digit in 4500 miles, you can round it to the nearest thousand, which would be 5000 miles. The most significant digit in this estimate is 5. Therefore, when considering the estimated digit, it would be 5.
um, about 4500
4500 of them.
There need no be any estimated digit.
4500
The last digit is always the estimated digit in a number
There are 4500 such numbers.
There need not be any estimated digit but, if there must be one, then it is the last digit: 3.
500
4500
10,800