To round to the tenths place, check the digit in the hundredths place.
If that digit is less than five, round down.
If that digit is five or more, round up.
The digit in the hundredths place is 5, so round up to 93.5.

To round to the hundredths place, check the digit in the thousandths place.
If that digit is less than five, round down.
If that digit is five or more, round up.
The digit in the thousandths place is 7, which is greater than five.
So, round up to 57.59.

First, round both numbers to the nearest hundred.

6,391	→	6,400
605	→	600

Then, subtract.

The actual difference of 6,391 and 605 is 5,786.
So, 5,800 is a good estimate of the difference.

One way to estimate the quotient is to round the dividend to the nearest thousand before dividing.

First, round the dividend to the nearest thousand.

4,978

→

5,000

Then, divide.