Calculate the Sum: Solving 13 + 2 + 8 Step by Step

Q: Does the order I add really not matter?

That's right! The commutative property says $ a+b+c $ equals the same no matter what order you use. Try it: $ 13+2+8 = 2+13+8 = 8+2+13 $ - all equal 23!

Q: What if none of the numbers make 10?

Look for other easy combinations! Numbers that end in 5+5, doubles like 4+4, or pairs that make multiples of 10. If nothing jumps out, just add left to right - that works perfectly too.

Q: How can I get faster at mental addition?

Practice spotting number bonds to 10 like 1+9, 2+8, 3+7, 4+6, 5+5. Also learn doubles: 6+6=12, 7+7=14, etc. These patterns make addition much quicker!

Q: Should I always reorder the numbers?

Not always! Only reorder if you see an easier path. For $ 13+2+8 $, grouping 2+8 helps. But for $ 12+3+4 $, left-to-right might be just as easy.

Addition Properties with Order Strategies

$13+2+8=$

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Solve

00:02 We will use the substitution law and solve the previous simple addition, let's continue

00:05 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

$13+2+8=$

Step-by-step solution

We will use the commutative property and first solve the addition exercise on the right:

$2+8=10$

Now we get:

$13+10=23$

Final Answer

Key Points to Remember

Essential concepts to master this topic

Rule: Addition can be done in any order using commutative property
Technique: Group easier pairs first, like $2+8=10$ , then add remaining numbers
Check: Verify by adding left to right: $13+2+8 = 15+8 = 23$ ✓

Common Mistakes

Avoid these frequent errors

Adding from left to right without considering easier combinations
Don't just add 13+2=15, then 15+8=23 without thinking! This works but misses easier paths like 2+8=10 first. Always look for number pairs that make 10 to simplify mental math.

Practice Quiz

Test your knowledge with interactive questions

$$ 100-(30-21)= $$

FAQ

Everything you need to know about this question

Why add 2+8 first instead of 13+2?

Adding numbers that make 10 is easier for mental math! Since $2+8=10$ , you get a nice round number. Then $13+10=23$ is much simpler than $15+8$ .

Does the order I add really not matter?

That's right! The commutative property says $a+b+c$ equals the same no matter what order you use. Try it: $13+2+8 = 2+13+8 = 8+2+13$ - all equal 23!

What if none of the numbers make 10?

Look for other easy combinations! Numbers that end in 5+5, doubles like 4+4, or pairs that make multiples of 10. If nothing jumps out, just add left to right - that works perfectly too.

How can I get faster at mental addition?

Practice spotting number bonds to 10 like 1+9, 2+8, 3+7, 4+6, 5+5. Also learn doubles: 6+6=12, 7+7=14, etc. These patterns make addition much quicker!

Should I always reorder the numbers?

Not always! Only reorder if you see an easier path. For $13+2+8$ , grouping 2+8 helps. But for $12+3+4$ , left-to-right might be just as easy.

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