Skip Counting & Rounding to 1000
Lessons in this chapter
About Skip Counting & Rounding to 1000
Playing with Numbers does two jobs that look unrelated and are not: both are about seeing numbers in groups rather than one at a time.
Skip Count Numbers up to 3-Digit Forward and Backward by 2 and 3 adds two things to 1st grade's skip counting. Counting backwards is genuinely harder than forwards, and counting by 3 breaks the comfortable patterns of 2, 5 and 10, where the last digit told you what came next.
Skip Count Numbers up to 3-Digit Forward and Backward by 5, 10 and 100 extends the familiar steps into the hundreds. Counting by 100 is the easiest sequence in the chapter and the most revealing, because only one digit moves, which shows the place value idea working.
Round Numbers up to 3-Digit to the Nearest Ten and then to the Nearest Hundred introduce the first deliberately approximate answer kids meet. The rule is mechanical, look at the next digit, but the purpose is not: rounding is how you check whether an answer is sensible, which is what the estimation lesson in the next chapter uses it for.
Skip Count Numbers up to 3-Digit Forward and Backward by 2 and 3 and Round Numbers up to 3-Digit to the Nearest Ten each come with their own worksheet, worked in the page and marked question by question. Four lessons, four sets of practice, with the counting deliberately settled before any rounding is asked for. All four are free to practice online.
Frequently asked questions
Skip counting forward and backward in 3-digit numbers, first by 2 and 3 and then by 5, 10 and 100, followed by rounding 3-digit numbers to the nearest ten and then to the nearest hundred. The skip counting sits in Number and Operations in Base Ten (2.NBT). Rounding is not asked for by the Common Core until 3rd grade, where it appears in 3.NBT; it is taught here because skip counting by tens and hundreds makes it easy to see.
Replacing a number with a nearby simpler one. 372 rounds to 370 to the nearest ten and to 400 to the nearest hundred.
Look at the digit to the right of the place you are rounding to. If it is 5 or more, round up; if it is less than 5, round down.
To check whether an answer is reasonable. If 372 + 215 is roughly 400 + 200, an answer of 5,870 is obviously wrong without redoing the sum.
Because the counting sequence is learned in one direction. Going backwards means working each step out rather than reciting, which is also why it helps subtraction.
Because 2, 5 and 10 all have a pattern in the last digit, so kids can follow them without really counting. Threes have no such shortcut, which makes it genuine practice.