We practice rounding 4-digit numbers to various places (to the nearest ten, nearest hundred, and nearest thousand). I explain a systematic method for rounding: draw a cutoff line right after the digit you're rounding to. Then look at the digit AFTER that line... if that digit is 0-4, round down. If that digit is 5-9, round up.
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Bar models in addition and subtraction — video lesson
Math Mammoth Grade 4 curriculum