Model Mixed Number Measurement Conversions on a Number Line
This Grade 4 Eureka Math skill teaches students to use a double number line to model and solve mixed number measurement conversions. The top scale shows the larger unit (e.g., hours, pounds) and the bottom scale shows the equivalent smaller unit (e.g., minutes, ounces). To convert 2 and 1/2 hours to minutes, students locate 2.5 on the hours scale and read off 150 on the minutes scale — calculated as 120 + (1/2 × 60). This visual strategy, from Chapter 36 of Eureka Math Grade 4, makes the fractional part of conversions concrete and intuitive.
Key Concepts
A double number line can be used to model the conversion of mixed number measurements. The top line is labeled with the larger unit, and the bottom line is labeled with the corresponding values in the smaller unit, creating a visual scale for conversion.
Common Questions
What is a double number line used for in measurement conversions?
A double number line shows two related units simultaneously — larger units on top and smaller units on bottom — so you can visually locate any mixed number on the top scale and read its equivalent on the bottom.
How do you convert 2 and 1/2 hours to minutes using a double number line?
Draw a number line with hours (0,1,2,3) on top and minutes (0,60,120,180) on bottom. Find 2.5 on the top scale — it falls halfway between 120 and 180 on the bottom, which is 150 minutes.
How do you convert 1 and 3/4 pounds to ounces?
Mark pounds (0,1,2) on top and ounces (0,16,32) on bottom. The point 1 and 3/4 falls between 16 and 32. Calculate: 16 + (3/4 × 16) = 16 + 12 = 28 ounces.
Why use a double number line instead of just multiplying?
The double number line makes the fractional part of a mixed number conversion visual and concrete, helping students see the proportional relationship between the whole and fractional parts of the measurement.
What should you label on each scale of the double number line?
Label the top scale with the larger unit starting from 0, marking whole number increments. Label the bottom scale with the corresponding smaller unit values at each whole-number tick mark.