3.6 Small Group · Group 1
Second Practice Form · Re-Teach, Homework or Retake · Same Standard, New Problems
Convert Measurements within the Same System · Conversion factor · Procedural Fluency · Real-World Applications
- Two measurements can only be compared when they are written in the same unit. Converting uses a special ratio — a unit ratio — that says how much of the smaller unit fits into exactly 1 of the larger unit. We'll walk through a worked example, try one together, then you'll try a few with hints right there when you need them.
- A ride requires riders to be at or above 44 inches tall. A child is 4 feet tall. The two measurements use different units, so I cannot compare them yet.
- Both units belong to the customary system, and there are 12 inches in one foot. That relationship is the conversion factor. As a ratio it is 12 : 1 — a unit ratio, because it compares an amount to exactly 1 foot.
- Inches are smaller than feet, so there will be MORE of them: I multiply. 4 × 12 = 48.
- The child is 48 inches tall. Now the comparison is fair: 48 inches is greater than 44 inches, so the child can go on the ride.
- Convert Measurements within the Same System (Convertir medidas dentro del mismo sistema) — Rewriting a measurement in a different unit of the SAME system, such as feet into inches or liters into milliliters.
- Conversion factor (Factor de conversión) — The ratio that links two units in the same measurement system, such as 12 inches to 1 foot. Within one system it is exact.
- Unit ratio (Razón unitaria) — A ratio that compares an amount to exactly 1 unit of another quantity, like 12 inches to 1 foot.
- Convert (Convertir) — To change a measurement from one unit to another without changing how much it is.
- Measurement system (Sistema de medidas) — A family of units that go together — customary units like inches and feet, or metric units like milliliters and liters.
- Double number line (Recta numérica doble) — Two number lines lined up so matching tick marks show two units for the same amount.
- A common mistake when converting within a measurement system is choosing the operation by habit instead of by unit size — multiplying every time. Converting 36 inches to feet by multiplying gives 36 × 12 = 432 feet, taller than a 40-story building. Ask first which unit is smaller: it takes MORE small units to make the same amount, so going to a smaller unit multiplies, and going to a larger unit divides.
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1 MULTIPLE CHOICE
Diamond needs 4 liters of water. Her bottle holds 500 milliliters. How many times must she fill it?
- A8 times
- B4 times
- C2 times
- D40 times
✏️ Workspace & Solution Steps -
2 MULTIPLE CHOICE
How many inches are in 2 feet?
- A24
- B14
- C10
- D12
✏️ Workspace & Solution Steps -
3 MULTIPLE CHOICE
How many liters is 2,000 milliliters?
- A2 L
- B2,000 L
- C200 L
- D20 L
✏️ Workspace & Solution Steps -
4 MULTIPLE CHOICE
Which pair belongs to the SAME measurement system?
- ACups and quarts
- BInches and centimeters
- CPounds and grams
- DLiters and gallons
✏️ Workspace & Solution Steps
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5 ERROR ANALYSIS
Find the error
- 1Setup:Convert 5 feet to inches.
- 2Step 1:There are 12 inches in 1 foot.
- 3Step 2:5 ÷ 12 = 0.42
- 4Step 3:So 5 feet is about 0.42 inches.
Which step contains the error? Explain the mathematical misconception and write the correct calculation below.
✏️ Corrected Mathematical Work & Explanation -
6 OPEN RESPONSE
Michael's mother is setting four fence posts. Each post needs 250 ounces of concrete mix, one bag holds 80 ounces, and each bag needs 1 quart of water. How many bags and how many cups of water does she need? Show your conversions.
✏️ Mathematical Justification & Response
Writing Task: Justify why your mathematical solution is accurate and complete.