0.21
0.2099
Two decimal places is the second 0 in the number ~0.2099
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You look at the number next to it which in this case is 9 ~0.2099
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If the number is 4 or less you round it down to 0 and if the number is five or more you round it up to 10, so 9 rounded is 10 because it’s bigger than 5
10 is carried along to make 0.2100 and that can be simplified down to 0.21 because you don’t need the 0’s necessarily