Adding several two-digit numbers
Add up to four two-digit numbers using strategies based on place value and properties of operations
What a learner can do afterwards
- Add three or four two-digit numbers by grouping tens and ones
- Look for pairs that make multiples of 10 to simplify addition
- Explain the strategy used to combine multiple addends
1 · Read
Sometimes you need to add three or four two-digit numbers, like 14 + 23 + 32 + 19. Adding them one at a time from left to right works, but it gets confusing fast. A better way is to split each number into its tens and ones. Add all the tens together, then add all the ones together. Last, add those two totals to get your answer.
Mia adds 14 + 23 + 32 + 19. First she adds the tens: 10 + 20 + 30 + 10 = 70. Then she adds the ones: 4 + 3 + 2 + 9 = 18. Last, she adds those two totals: 70 + 18 = 88.
Before you add everything in order, scan the ones digits for a pair that makes 10. For example, 16 and 24 have ones digits 6 and 4, and 6 + 4 = 10. So 16 + 24 = 40 exactly. Pairing numbers like this first can make the whole sum easier.
Split into tens and ones, add each group, then combine, and look for pairs that make ten along the way.
More to read
Whole numbers in expanded form review
Expanded form is a way to write a number by showing the value of each digit. The number 46 is really 40 + 6. The 4 is in the tens place, so it means 4 tens, or 40. The 6 is in the ones place, so it means 6 ones. Why does this help when you add? Because you can break every number into tens and ones, add the tens, add the ones, and then put it all back together. Try it with 32 + 45. Write 32 as 30 + 2 and 45 as 40 + 5. Add the tens: 30 + 40 = 70. Add the ones: 2 + 5 = 7. Now put them together: 70 + 7 = 77. When you add three or four numbers, expanded form is even handier. Break each one apart, gather all the tens, gather all the ones, and combine. You can even swap the pieces around, because adding in any order gives the same total. That is a property of addition.
Adding and Subtracting Within 100 Using Place Value Strategies
This lesson is about adding numbers up to 100 by thinking about tens and ones. Every two-digit number is made of tens and ones. The number 58 is 5 tens and 8 ones. When you add numbers, you can break them apart into tens and ones first. Then add the tens together, and add the ones together. If the ones add up to 10 or more, group 10 ones into 1 ten. Drawing can help too. You can draw sticks for tens and dots for ones. Then you can see the numbers and move the pieces around. Moving pieces around is fine, because addition lets you add in any order. Look for numbers whose ones make 10, like 37 and 43. Putting those together first makes a friendly number, and friendly numbers are easy to add. Practice by adding pairs like 46 + 27, then try three numbers, and then four. The more you practice breaking numbers apart, the faster your brain gets at seeing the tens and ones hiding inside every number.
2 · Watch
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Where this leads
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11 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.