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I am working on lesson creation for Learn Zillion. When looking at 2.NBT.8, it states, “CCGPS.2.NBT.8 Mentally add 10 or 100 to a given number 100–900, and mentally subtract 10 or 100 from a given number 100–900.”
One of the unpacked document mentions that this also expands to multiples of 10 and crossing centuries. When creating lessons, should we only focus on adding and subtraction 10 and 100, or does it imply and expand into teaching adding and subtracting multiples of 10 such as 243 + 30 and 473 + 400?
Also, does this standard address crossing centuries in problems such as 274 + 40?
I’m not sure which unpacked document you are talking about, do you mean the NBT Progressions document? Anyway, to answer your question, I think it is limited to what it says, just adding 10 or 100. Notice that it is about mental computation only. In 2.NBT.7 students are expected to add and subtract within 1000, so that certainly includes 243 + 30 and 472 + 400. But this standard is about mental work only. The point is not so much computation as encouraging a clear understanding of the base ten system. If a student can add 10 mentally to 243, then adding 30 is more cognitively demanding but doesn’t show a better grasp of the base ten system.
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