Subtract 18 from 27 Using Base-10 Blocks: Visual Mathematics

Subtraction with Base-Ten Regrouping

If we have 27 blocks in total and we remove 18 of those blocks, how many blocks remain? Remember you can break down a row of 10 blocks into single units.

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Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

If we have 27 blocks in total and we remove 18 of those blocks, how many blocks remain? Remember you can break down a row of 10 blocks into single units.

2

Step-by-step solution

To solve this problem, begin by employing the basic subtraction formula:

  • Subtract the blocks removed (18) from the total number of blocks (27).
  • Mathematically, this is written as: 2718 27 - 18 .

Perform the subtraction:

2718=927 - 18 = 9.

Therefore, the number of blocks remaining after removing 18 from 27 is 9\boxed{9}.

3

Final Answer

9 9

Key Points to Remember

Essential concepts to master this topic
  • Rule: When subtracting, start from the ones place and move left
  • Technique: Break ten-blocks into ones when needed: 27 = 2 tens + 7 ones
  • Check: Count remaining blocks or add back: 9 + 18 = 27 ✓

Common Mistakes

Avoid these frequent errors
  • Not understanding place value when regrouping
    Don't treat all blocks as individual units without recognizing ten-blocks = wrong counting! This leads to confusion about which blocks to remove. Always identify tens and ones first, then regroup systematically.

Practice Quiz

Test your knowledge with interactive questions

If we have 67 blocks in total, how many blocks will remain if we remove 5 tens and 4 ones?

FAQ

Everything you need to know about this question

Why can't I just count all 27 blocks individually?

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You absolutely can! But understanding place value (2 tens + 7 ones) makes subtraction easier and prepares you for larger numbers. Both methods give the same answer.

When do I need to break apart a ten-block?

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Break apart a ten-block when you don't have enough individual units to subtract from. In this problem, you have 7 ones but need to subtract 8 ones from 18.

How do I know which blocks to remove first?

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Start by removing as many complete ten-blocks as possible (remove 1 ten-block for 10 of the 18). Then remove individual ones for the remaining amount.

What if I get confused with the visual blocks?

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Try the standard algorithm: 2718 27 - 18 . Since 7 < 8, borrow from the tens place: 178=9 17 - 8 = 9 , and 11=0 1 - 1 = 0 .

How can I check my answer is correct?

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Add back method: 9+18=27 9 + 18 = 27 ✓ Or count remaining blocks: You should see exactly 9 blocks left in the diagram.

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