Question

how do you determine which number is in the thousandths place of 1,356.209

Answer 1

1356.209 is the number

1 is in the thousands place
3 is in the hundreds place
5 is in the tens place
6 is in the units (ones) place

Then, there is a decimal point.

2 is in the tenths place (2 ÷ 10 = 0.2)
0 is in the hundredths place (0 ÷ 100 = 0)
9 is in the thousandths place (9 ÷ 1000 = 0.009)
When we add 0.2 + 0 + 0.009, we get 0.209
  0.200
+0.000
+0.009
-----------
  0.209

I hope this helps.