Solve the Equation: Finding the Missing Number in 81 + __ = 98

Addition Equations with Number Line Jumps

Solve the addition exercise,

using two jumps on the number line below:

81+=98 81+\Box=98

818181989898

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Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve the addition exercise,

using two jumps on the number line below:

81+=98 81+\Box=98

818181989898

2

Step-by-step solution

To solve the problem 81+=9881 + \Box = 98 using two jumps along a number line, follow these steps:

  • Step 1: Start at 81 on the number line.
  • Step 2: Make the first jump from 81 to the next convenient round number: 90.
  • Step 3: Calculate the increase from 81 to 90: 9081=990 - 81 = 9.
  • Step 4: Make the second jump from 90 to 98.
  • Step 5: Calculate the increase from 90 to 98: 9890=898 - 90 = 8.
  • Step 6: Add both jumps to determine the total required increment: 9+8=179 + 8 = 17.

The total increment needed to go from 81 to 98 using two jumps is 1717.

Therefore, the solution to the problem is =17\Box = 17.

3

Final Answer

17 17

Key Points to Remember

Essential concepts to master this topic
  • Strategy: Break the jump into two convenient steps using landmarks
  • Technique: Jump 81 → 90 (add 9), then 90 → 98 (add 8)
  • Check: Add both jumps: 9 + 8 = 17, verify 81 + 17 = 98 ✓

Common Mistakes

Avoid these frequent errors
  • Trying to solve in one jump without landmarks
    Don't jump directly from 81 to 98 without using helpful numbers like 90 = harder mental math and more errors! This makes counting difficult and leads to mistakes. Always break big jumps into smaller, easier steps using round numbers as landmarks.

Practice Quiz

Test your knowledge with interactive questions

If we have 85 blocks in total, how many blocks will remain if we remove 4 tens and 1 one?

FAQ

Everything you need to know about this question

Why can't I just count from 81 to 98?

+

You absolutely can! But using two jumps with landmarks makes it much easier and less prone to counting errors. It's like taking rest stops on a long trip.

How do I choose good landmark numbers?

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Pick round numbers like 90, 100, etc. that are close to your starting point. From 81, jumping to 90 first is natural because it's only 9 steps away!

What if I get different numbers for my two jumps?

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That's fine! You could jump 81 → 85 → 98 (jumps of 4 and 13). As long as your total adds up to 17, any combination works.

Do I have to use exactly two jumps?

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The problem asks for two jumps specifically, but you could use more if needed. Two jumps just makes it simpler and matches what the question requests.

How do I know my answer is right?

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Always check: 81+17=98 81 + 17 = 98 . If this equals the target number, you're correct! You can also verify that your two jump amounts add up to your final answer.

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