Solve 18 - 1 × 0.1: Order of Operations with Decimals

Multiplication Before Subtraction with Decimals

18−1×0.1= 18-1\times0.1=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:06 Let's solve this problem together!
00:10 Remember, do multiplication and division first, then addition and subtraction.
00:16 A number times one is always that same number.
00:20 Great! Let's keep going with the solution.
00:23 And there you go! That's how we solve this question.

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

18−1×0.1= 18-1\times0.1=

2

Step-by-step solution

According to the rules of the order of operations we should begin by placing the multiplication exercise within parentheses:

18−(1×0.1)= 18-(1\times0.1)=

We then proceed solve the multiplication exercise:

1×0.1=0.1 1\times0.1=0.1

And we should obtain the following exercise:

18−0.1=17.9 18-0.1=17.9

3

Final Answer

17.9

Key Points to Remember

Essential concepts to master this topic
  • PEMDAS Rule: Always perform multiplication operations before subtraction
  • Technique: Calculate 1 × 0.1 = 0.1 first, then subtract
  • Check: Verify 18 - 0.1 = 17.9 by adding back: 17.9 + 0.1 = 18 ✓

Common Mistakes

Avoid these frequent errors
  • Working left to right without following order of operations
    Don't calculate 18 - 1 = 17 first and then multiply by 0.1 = 1.7! This ignores PEMDAS and gives the wrong answer. Always multiply first: 1 × 0.1 = 0.1, then subtract: 18 - 0.1 = 17.9.

Practice Quiz

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\( 100+5-100+5 \)

FAQ

Everything you need to know about this question

Why can't I just work from left to right like reading?

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Mathematics has a specific order of operations (PEMDAS) that must be followed! Working left to right gives 18 - 1 = 17, then 17 × 0.1 = 1.7, which is completely wrong.

What does PEMDAS mean for this problem?

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PEMDAS stands for Parentheses, Exponents, Multiplication/Division, Addition/Subtraction. Since we have multiplication and subtraction, we do multiplication first: 1×0.1=0.1 1 \times 0.1 = 0.1

How do I remember to multiply decimals correctly?

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When multiplying by 0.1, you're multiplying by one-tenth. So 1×0.1=0.1 1 \times 0.1 = 0.1 (one-tenth of 1). Count decimal places: 0.1 has 1 decimal place, so your answer has 1 decimal place.

What if I put parentheses around the multiplication?

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Great thinking! Writing 18−(1×0.1) 18 - (1 \times 0.1) makes the order of operations crystal clear. The parentheses don't change the answer, but they help you see what to calculate first.

How can I check if 17.9 is really correct?

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Use the inverse operation! Add the number you subtracted back: 17.9+0.1=18 17.9 + 0.1 = 18 ✓. You get back to your original number, so 17.9 is correct!

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