Common Mistakes: Measurement Conversions
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Even careful students make mistakes with measurement conversions! Let's learn about common errors so you can avoid them.
Mistake #1: Multiplying When You Should Divide (or Vice Versa)
Wrong: How many feet is 36 inches? 36 × 12 = 432 feet
Right: 36 ÷ 12 = 3 feet
Remember: Going from SMALL to BIG units = DIVIDE. Going from BIG to SMALL units = MULTIPLY.
Mistake #2: Using the Wrong Conversion Factor
Wrong: How many inches in 4 feet? 4 × 3 = 12 inches (using yards instead of feet)
Right: 4 × 12 = 48 inches (12 inches = 1 foot)
Always check which units you're converting between!
Mistake #3: Forgetting Units in Your Answer
Wrong: 3 hours = 180
Right: 3 hours = 180 minutes
Always label your answer with the correct unit!
Practice: Find the Mistake
1. A student converted 5 feet to inches by dividing: 5 ÷ 12 = 0.4 inches. What did they do wrong?
A) Nothing, 0.4 inches is correct
B) They should have multiplied, not divided
C) They used the wrong number
D) They forgot the units
Answer
B) - Feet to inches is big to small, so multiply: 5 × 12 = 60 inches.
2. To convert 240 minutes to hours, a student wrote: 240 × 60 = 14,400 hours. What's wrong?
A) Nothing is wrong
B) Should have divided instead of multiplied
C) Used 60 instead of 24
D) Forgot the units
Answer
B) - Minutes to hours is small to big, so divide: 240 ÷ 60 = 4 hours.
3. Which conversion factor should you use to convert yards to feet?
A) 12 (inches in a foot)
B) 3 (feet in a yard)
C) 100 (centimeters in a meter)
D) 60 (minutes in an hour)
Answer
B) - There are 3 feet in 1 yard.
4. A student says 72 inches equals 6 yards. What did they do wrong?
A) Nothing, 6 yards is correct
B) They converted inches to feet, not yards
C) They divided when they should multiply
D) They used the wrong conversion factor
Answer
B) - 72 ÷ 12 = 6 feet, not yards. To get yards: 6 feet ÷ 3 = 2 yards.
5. Converting from hours to minutes, should you multiply or divide by 60?
A) Multiply, because hours are bigger than minutes
B) Divide, because hours are bigger than minutes
C) Multiply, because 60 is a big number
D) It doesn't matter
Answer
A) - Big to small = multiply. 1 hour = 60 minutes, so 3 hours = 3 × 60 = 180 minutes.
6. A student converted 2 days to hours: 2 × 60 = 120 hours. What's the error?
A) Should have divided
B) Used 60 (minutes) instead of 24 (hours in a day)
C) Nothing is wrong
D) Forgot the units
Answer
B) - Days to hours uses 24, not 60. Correct: 2 × 24 = 48 hours.
7. How can you check if your conversion answer makes sense?
A) The number should always get bigger
B) The number should always get smaller
C) More small units should give a bigger number; fewer big units should give a smaller number
D) Just trust your calculator
Answer
C) - 2 feet = 24 inches (bigger number of smaller units), 24 inches = 2 feet (smaller number of bigger units).
8. A student wrote "3 meters = 300." What's missing?
A) The calculation
B) The unit (centimeters)
C) Nothing is missing
D) The conversion factor
Answer
B) - The answer should be "300 centimeters" - always include units!
9. To convert 9 feet to yards, a student multiplied: 9 × 3 = 27 yards. Is this correct?
A) Yes, 27 yards is correct
B) No, should divide: 9 ÷ 3 = 3 yards
C) No, should use 12 instead of 3
D) No, should use 36 instead of 3
Answer
B) - Feet to yards is small to big = divide. 9 ÷ 3 = 3 yards.
10. What's the best way to remember when to multiply vs divide?
A) Always multiply
B) Always divide
C) Big to small = multiply, Small to big = divide
D) It depends on the day
Answer
C) - This rule always works: Big to small = multiply (more smaller units), Small to big = divide (fewer bigger units).
Next Steps
- Always check if your answer makes sense
- Remember: Big to small = multiply, Small to big = divide
- Always include units in your answer
- Continue to the Unit Quiz