We have a decimal system, which means that each column of our number system has a value of increasing powers of ten as you move from right to left. And each column is of decreasing powers of ten as you move from left to right.
10^n....10^2, 10^1, 10^0 (decimal point) 10^-1, 10^-2....10^-n
So the decimal point marks the transition to negative powers...
10^n, 100, 10, 1 (decimal point) 1/10, 1/100...1/10^n
All of this was the long way of explaining that the first place after the decimal point is the tenths column so if you have 3 tenths, you have 0.3...In this case you have 17 3/10 so
17.3
