7th Grade Task: National Debt

Essential and guiding questions:

How large is the national debt? Does the number of boxcars full of jelly beans give an accurate picture of the size of this number? Why?
Did you have to approximate anything? How did approximations affect your answers?
Why did you need to use conversions from one unit to another?
How accurate was your initial guess in part (b)? Were you surprised by the actual answer? Why?How large is the national debt? Does the number of boxcars full of jelly beans give an accurate picture of the size of this number? Why?
Did you have to approximate anything? How did approximations affect your answers?
Why did you need to use conversions from one unit to another?
How accurate was your initial guess in part (b)? Were you surprised by the actual answer? Why?

Blooms taxonomy level:

Understanding

Extension suggestions:

If students finish early….

A good estimate of the length of one of your boxcars is 52 feet. If we count only the boxcars holding jelly beans (and ignore the engines we would need to pull the train), how long will the train be in feet? In miles? (Note: To compute the length of the train, the students will need to know how many feet are in one mile. Note also that the system of units has changed in this question (from metric to U.S. standard).
The inside boxcar dimensions used for this problem are: Length: 15.4 m (~50.52 feet); Width: 3.98 m (~13.06 feet); and Height: 2.90 m (~9.51 feet). The 52 feet outside length is an estimate for this car. Using the numbers calculated in this problem, the train would be approximately 3,275 miles long.)
When we worked the problem, we assumed the jelly beans were packed tightly with no air space between them. Typically, between 20% and 30% of the volume is lost to air space between the jelly beans. If we take this into account, how will this affect your answer for the number of boxcars needed?

Advancing Questions:

How would you calculate the length of your train?
How do you convert from feet to miles?
Why are you losing volume to air? How would you calculate how much of your volume is taken by air instead of jelly beans?

Assessing Questions:

How long is your train in miles? Can you describe a good way to think about how long this train really is?
How did you take the air space into account? What calculations did you use? Why did you choose that strategy?

Originator: