Five pages on changing a three-digit number by 10 or 100, the mental math behind adding within 1,000. Page 1 shows a number in base-ten blocks (flats, rods and cubes): students write the number, then 10 less, 10 more, 100 less and 100 more in a small table. Page 2 is arrow chains (+10, -10, +100, -100) where some steps cross a hundred, such as 396 + 10 = 406 or 203 - 10 = 193. Page 3 is a table of twelve numbers from 100 to 900 to finish in your head. Page 4 starts from a fact students know (3 + 4 = 7, so 30 + 40 = 70 and 300 + 400 = 700), then adds and takes away hundreds or tens (450 + 30, 964 - 500), two with a missing number; only one place changes. Page 5 hops on an open number line, by hundreds and then one hop for the tens (340 + 230: 440, 540, 570). Each page starts with a worked example.
Before page 1, build 245 with blocks and add one rod at a time, saying the numbers aloud. Then add a flat and ask which digit changed. Page 2 is the place to stop and talk: what happens to 396 when you add 10? Let students build it and trade before they write 406.
Say a number like 352 and take turns: one says 10 more, the other 100 less. Money works too: $3.52 and one more dime, or one more dollar.
This pack supports the following Common Core State Standards for Mathematics:
© Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
A 5-page 2nd grade pack for finding 10 more, 10 less, 100 more and 100 less than three-digit numbers, then adding and subtracting hundreds and tens. Read a number in base-ten blocks and write its four neighbors, follow arrow chains that cross a hundred (396 + 10 = 406), and fill in a table in your head. Use a fact you know (3 + 4 = 7, so 300 + 400 = 700) to add and take away hundreds and tens, and hop by hundreds and then the tens on an open number line (340 + 230). Every page comes in color and in black and white. Answer keys included.
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