โ Math ยท Numbers and Algebra ยท Lesson 3 of 8 ยท 6 min
Order of operations, negative numbers and absolute value
๐งฎ Two people can work 8 โ 2 ร 3 and get 18 and 2. Only one of them gets the point on test day.
๐ก Key idea
PEMDAS, with multiplication/division and addition/subtraction each worked left to right as pairs.
๐ง The idea
The ORDER OF OPERATIONS is PEMDAS: Parentheses (and other grouping) first, then Exponents, then Multiplication and Division from left to right, then Addition and Subtraction from left to right. Multiplication does not always beat division; whichever comes first reading left to right goes first: 12 รท 3 ร 2 = 4 ร 2 = 8. With NEGATIVE NUMBERS, adding a negative is subtracting (5 + (โ8) = โ3), and subtracting a negative is adding (5 โ (โ8) = 13). When you multiply or divide, two signs that match give a positive and two signs that differ give a negative: (โ4)(โ3) = 12, but (โ4)(3) = โ12. Watch exponents: (โ3)ยฒ = 9, but โ3ยฒ = โ9, because the exponent applies only to the 3. ABSOLUTE VALUE, written |x|, is a number's distance from zero, so it is never negative: |โ7| = 7. Treat the bars like parentheses and work inside them first.
โ๏ธ Worked example
Evaluate 18 โ 3 ร (4 โ 6)ยฒ รท 2.
Step 1: Parentheses: 4 โ 6 = โ2.
Step 2: Exponent: (โ2)ยฒ = 4.
Step 3: Multiply and divide left to right: 3 ร 4 = 12, then 12 รท 2 = 6.
Step 4: Subtract: 18 โ 6 = 12.
Answer: 12.
๐ Takeaways
- Parentheses, exponents, then ร รท left to right, then + โ left to right.
- Subtracting a negative is adding; matching signs multiply to a positive.
- Absolute value is distance from zero, never negative.
๐ Terms in this lesson
Order of operations: The rule for evaluating expressions: parentheses, exponents, multiplication and division left to right, then addition and subtraction left to right; for example, 2 + 3 ร 4 = 14.
โ Check yourself
Question 1 of 3
What is 20 โ 4 ร 3 + 2?
- 50
- 10
- 14
- 6
Show the answer and rationale
Answer: B
Multiply first: 4 ร 3 = 12. Then work left to right: 20 โ 12 = 8, and 8 + 2 = 10. The answer 50 subtracts first (16 ร 3 + 2), and 6 adds 12 + 2 before subtracting, breaking the left-to-right rule.
Question 2 of 3
What is โ6 โ (โ10)?
- 4
- 16
- โ16
- โ4
Show the answer and rationale
Answer: A
Subtracting a negative is adding: โ6 + 10 = 4. The answer โ16 treats the expression as โ6 โ 10, and โ4 gets the size right but the sign wrong.
Question 3 of 3
What is |3 โ 11| โ |โ2|?
- 6
- โ6
- 10
- โ10
Show the answer and rationale
Answer: A
Work inside the bars first: |3 โ 11| = |โ8| = 8 and |โ2| = 2. Then 8 โ 2 = 6. The answer 10 adds the absolute values, and โ10 forgets that absolute value is never negative.
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