Solve Sequential Subtraction: 78 - 29 - 19 Step by Step

Sequential Subtraction with Two-Digit Numbers

782919=78 - 29 - 19 =

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1

Understand the problem

782919=78 - 29 - 19 =

2

Step-by-step solution

First, subtract 29 from 78: 7829=4978 - 29 = 49.

Next, subtract 19: 4919=3049 - 19 = 30.

The final answer is 3030.

3

Final Answer

30 30

Key Points to Remember

Essential concepts to master this topic
  • Order Rule: Work left to right with subtraction operations
  • Technique: First calculate 78 - 29 = 49, then 49 - 19
  • Check: Add back: 30 + 19 + 29 = 78 ✓

Common Mistakes

Avoid these frequent errors
  • Subtracting smaller numbers from larger numbers instead of following order
    Don't rearrange to 78 - 19 - 29 thinking it's easier = wrong answer of 30! Order matters in subtraction unlike addition. Always work strictly from left to right: 78 - 29 first, then subtract 19.

Practice Quiz

Test your knowledge with interactive questions

Solve the following equation:

\( 12+7-5\text{ }= \)

FAQ

Everything you need to know about this question

Why can't I subtract 19 from 78 first since it's easier?

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Because subtraction is not commutative like addition! The order matters. 78 - 29 - 19 means start with 78, subtract 29, then subtract 19 from that result.

Can I add the numbers I'm subtracting first?

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Yes! You can think of it as 78 - (29 + 19) = 78 - 48 = 30. This works because subtracting two amounts is the same as subtracting their sum.

How do I check if my answer is correct?

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Add everything back together! Start with your answer and add the numbers you subtracted: 30 + 19 + 29 = 78. If you get the original number, you're right!

What if I get a negative number?

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That means you're subtracting more than you started with. Double-check your calculations - you might have made an error in borrowing or place value.

Is there a faster way to do this mentally?

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Yes! Round to make easier numbers: 78 - 30 - 20 = 28, then add back the extra amounts you subtracted: 28 + 1 + 1 = 30.

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