To find the smallest decimal, compare place values left to right: tenths, hundredths, thousandths.

Numbers	=	0.600, 0.156, 0.510, 0.165
All have ones digit 0. Compare tenths: 6, 1, 5, 1. 1 is smallest, so compare 0.156 and 0.165.
Compare hundredths: 0.156 has 5, 0.165 has 6. 5 < 6, so 0.156 is the smallest.
Smallest	=	0.156