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โž— Math ยท Numbers and Algebra ยท Lesson 3 of 8 ยท 6 min

Order of operations, negative numbers and absolute value

๐Ÿงฎ Two people can work 8 โˆ’ 2 ร— 3 and get 18 and 2. Only one of them gets the point on test day.

๐Ÿ’ก Key idea

PEMDAS, with multiplication/division and addition/subtraction each worked left to right as pairs.

๐Ÿง  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 + (โˆ’8) = โˆ’3), and subtracting a negative is adding (5 โˆ’ (โˆ’8) = 13). When you multiply or divide, two signs that match give a positive and two signs that differ give a negative: (โˆ’4)(โˆ’3) = 12, but (โˆ’4)(3) = โˆ’12. Watch exponents: (โˆ’3)ยฒ = 9, but โˆ’3ยฒ = โˆ’9, because the exponent applies only to the 3. ABSOLUTE VALUE, written |x|, is a number's distance from zero, so it is never negative: |โˆ’7| = 7. Treat the bars like parentheses and work inside them first.

โœ๏ธ Worked example

Evaluate 18 โˆ’ 3 ร— (4 โˆ’ 6)ยฒ รท 2.
Step 1: Parentheses: 4 โˆ’ 6 = โˆ’2.
Step 2: Exponent: (โˆ’2)ยฒ = 4.
Step 3: Multiply and divide left to right: 3 ร— 4 = 12, then 12 รท 2 = 6.
Step 4: Subtract: 18 โˆ’ 6 = 12.
Answer: 12.

๐Ÿ“Œ Takeaways

  • Parentheses, exponents, then ร— รท left to right, then + โˆ’ left to right.
  • Subtracting a negative is adding; matching signs multiply to a positive.
  • Absolute value is distance from zero, never negative.

๐Ÿ“– 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.

โœ… Check yourself

Question 1 of 3

What is 20 โˆ’ 4 ร— 3 + 2?

  1. 50
  2. 10
  3. 14
  4. 6
Show the answer and rationale

Answer: B

Multiply first: 4 ร— 3 = 12. Then work left to right: 20 โˆ’ 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 โˆ’6 โˆ’ (โˆ’10)?

  1. 4
  2. 16
  3. โˆ’16
  4. โˆ’4
Show the answer and rationale

Answer: A

Subtracting a negative is adding: โˆ’6 + 10 = 4. The answer โˆ’16 treats the expression as โˆ’6 โˆ’ 10, and โˆ’4 gets the size right but the sign wrong.

Question 3 of 3

What is |3 โˆ’ 11| โˆ’ |โˆ’2|?

  1. 6
  2. โˆ’6
  3. 10
  4. โˆ’10
Show the answer and rationale

Answer: A

Work inside the bars first: |3 โˆ’ 11| = |โˆ’8| = 8 and |โˆ’2| = 2. Then 8 โˆ’ 2 = 6. The answer 10 adds the absolute values, and โˆ’10 forgets that absolute value is never negative.

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