What's is 0.173 rounded to the nearest hundredth

0.17

because five or more goes up (hundredths is the second place after the decimal) but four or less goes down. so three stays at seven

five or more raise the score four or less let it rest

Round down if n<5, otherwise round up ...

In this case the hundredth place is 7 and the next place is 3. So we round down 3 to zero, or if you prefer we keep 7 the same leaving:

0.17