Addition and Subtraction Within 100
In 2nd grade, you become a NUMBER NINJA! You can now work with numbers all the way up to 100. Today you will learn three powerful strategies to add and subtract ANY pair of numbers under 100.
Place Value
Every two-digit number has two SPOTS:\n\n- The TENS place (on the left)\n- The ONES place (on the right)\n\nFor the number 47:\n- 4 is in the TENS place = 40\n- 7 is in the ONES place = 7\n- Together: 40 + 7 = 47\n\nKnowing place value makes adding and subtracting MUCH easier.
Strategy 1: Break Apart
To add 34 + 25:\n\n1. Break 34 into 30 + 4\n2. Break 25 into 20 + 5\n3. Add the tens: 30 + 20 = 50\n4. Add the ones: 4 + 5 = 9\n5. Put them together: 50 + 9 = 59\n\nBig number problem → small number problems!
Strategy 2: Number Line
Draw a number line. To solve 62 - 18:\n\n1. Start at 62\n2. Jump back 10 → 52\n3. Jump back 8 more → 44\n\n**62 - 18 = 44**. Big jumps for tens, small jumps for ones.
What is 47 + 30?
Strategy 3: Regrouping (Carrying)
When ones add to more than 10, you REGROUP:\n\nTo add 38 + 25:\n1. Ones: 8 + 5 = 13\n2. Thirteen is one ten + three ones. Write 3 in the ones place.\n3. CARRY the one ten over.\n4. Tens: 3 + 2 + 1 (carried) = 6\n5. Answer: 63\n\nThis is called "carrying the one."
Addition Race
With a grown-up:\n\n1. Use playing cards (no face cards).\n2. Each player flips 2 cards and makes a 2-digit number.\n3. Race to ADD your number to the other player's.\n4. Use Break Apart strategy if you need to.\n5. First to 10 wins!
Subtraction Story
1. Make up a word problem: "I had 62 stickers. I gave 18 away. How many do I have now?"\n2. Draw a picture to show it.\n3. Solve using Number Line strategy.\n4. Check: your answer plus 18 should be 62!\n5. Make another one, this time with your own numbers.
Solve: 54 + 29
Real-Life Math
You use 2-digit math EVERY DAY:\n\n- Counting your age + your sister's age\n- Adding your sticker collection\n- Checking how many minutes until dinner\n- Counting pennies, nickels, and dimes\n\nGood math is LIFE math.
Solve: 80 - 35
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