639.497 rounded to the nearest tenth

It is 639.5. this is how you round numbers to the nearest tenth: 

if the digit in the hundredths place is 5 or more you round up one, if it is lower than 5 it stays the same, pay no attention to the thousandths placeex--> 0.497 
the 4 is the tenths place 
th 9 is the hundredths place 
the 7 is the thousandths placesince 9 is 5 or more you round the 4 up one number, so the 4 would be a 5. pay no attention to the 7. lets do another 

0.426 
the 4 stays as a 4 because 2 is a lower number than 5.