This is a short activity with specific instructions that deals with the misconception that the decimal point is the "center" of the base ten system. The reality is that the decimal point has two functions, one of which is to act as a "pointer" to the ones place, which is the actual divider of the place value chart. This goes a long way towards explaining to your students why there is no "opposite" of the ones place: it is the actual center from which the decimals and whole numbers originate.
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