Subtract 7 from 45: Base-10 Block Decomposition Problem

Subtraction with Base-10 Decomposition

If we have 45 blocks in total and we remove 7 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 45 blocks in total and we remove 7 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, we'll adhere to a few simple steps:

  • Step 1: Identify the given numbers; initially, we have 45 45 blocks.
  • Step 2: Determine the number of blocks to remove, which is 7 7 .
  • Step 3: Subtract the removed blocks from the total: 457 45 - 7 .

Now, let's perform the calculation:
The difference between 45 45 and 7 7 can be found by performing the subtraction:
457=38 45 - 7 = 38 .

Therefore, after removing 7 7 blocks from 45 45 blocks, the number of blocks remaining is 38 38 .

Thus, the solution to the problem is 38 38 .

3

Final Answer

38 38

Key Points to Remember

Essential concepts to master this topic
  • Rule: Break down groups of 10 into individual units when needed
  • Technique: Calculate 457=38 45 - 7 = 38 by direct subtraction
  • Check: Count remaining blocks: 3 rows of 10 plus 8 singles = 38 ✓

Common Mistakes

Avoid these frequent errors
  • Adding instead of subtracting
    Don't add the numbers together like 45 + 7 = 52! The problem asks to 'remove' or 'subtract' blocks, not add more. Always read carefully: 'subtract 7 from 45' means 45 - 7.

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

When do I need to break down the blocks?

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You only need to break down blocks when you don't have enough single units to subtract from. In this problem, since we're subtracting 7 from 45, we can do it directly without breaking down any groups of 10.

How do I visualize 45 blocks?

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Think of 45 as 4 complete rows of 10 blocks plus 5 individual blocks. This gives you 40 + 5 = 45 total blocks to work with.

What if I need to subtract more than the single blocks I have?

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Then you'd need to 'borrow' by breaking down one group of 10 into 10 individual blocks. For example, if you had 32 blocks and needed to subtract 8, you'd break down one group of 10.

How can I double-check my answer?

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Add your answer back to what you subtracted: 38+7=45 38 + 7 = 45 . If you get the original number, your subtraction was correct!

Why is the answer 38 and not 35 or 47?

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38 is correct because 45 - 7 = 38. The other answers come from common mistakes: 35 might come from 45 - 10, and 47 might come from adding instead of subtracting.

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