Solve the Addition Problem: 8 + 2 + 7 = ?

Q: Why should I group 8 + 2 first instead of going left to right?

Great question! While left-to-right works, grouping 8 + 2 = 10 first gives you a nice round number. Then 10 + 7 = 17 is much easier to calculate mentally!

Q: Is there only one way to group these numbers?

Actually, you could also try 8 + 7 = 15, then 15 + 2 = 17. Both methods work! The key is finding what feels easiest for you.

Q: How can I check my answer without using a calculator?

Try counting up from one number! Start at 8, then count: 9, 10 (that's +2), then 11, 12, 13, 14, 15, 16, 17 (that's +7 more). You should land on 17!

Q: What makes 10 a friendly number for mental math?

Round numbers like 10 are easy to work with because our number system is based on 10! Adding to 10 is like just changing the ones digit: 10 + 7 = 17.

Addition Strategies with Three Numbers

$8+2+7=$ ?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:05 Let's solve this problem together!

00:08 We will follow the order of operations, moving from left to right.

00:13 And that's how we find the answer. Great job!

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

$8+2+7=$ ?

Step-by-step solution

First, solve the left exercise since adding the numbers together will give us a round number:

$8+2=10$

Now we have an easier exercise to solve:

$10+7=17$

Final Answer

Key Points to Remember

Essential concepts to master this topic

Strategy: Look for pairs that make round numbers first
Technique: Group 8 + 2 = 10, then add 7 easily
Check: Count all numbers together: 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 ✓

Common Mistakes

Avoid these frequent errors

Adding from left to right without grouping
Don't just compute 8 + 2 + 7 by going 8 + 2 = 10, then 10 + 7 = 17 mechanically! While this works, you miss the opportunity to use number sense strategies. Always look for friendly number pairs like 8 + 2 = 10 first to make mental math easier.

Practice Quiz

Test your knowledge with interactive questions

$$ 94+12+6= $$

FAQ

Everything you need to know about this question

Why should I group 8 + 2 first instead of going left to right?

Great question! While left-to-right works, grouping 8 + 2 = 10 first gives you a nice round number. Then 10 + 7 = 17 is much easier to calculate mentally!

What if I don't see any friendly pairs?

That's okay! You can always add from left to right. But with practice, you'll start noticing pairs that make 10, 20, 100 or other round numbers that make math easier.

Is there only one way to group these numbers?

Actually, you could also try 8 + 7 = 15, then 15 + 2 = 17. Both methods work! The key is finding what feels easiest for you.

How can I check my answer without using a calculator?

Try counting up from one number! Start at 8, then count: 9, 10 (that's +2), then 11, 12, 13, 14, 15, 16, 17 (that's +7 more). You should land on 17!

What makes 10 a friendly number for mental math?

Round numbers like 10 are easy to work with because our number system is based on 10! Adding to 10 is like just changing the ones digit: 10 + 7 = 17.

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