Tuesday, July 19, 2011

Was the Bus Empty When it Left the Terminal

Image from FreeFoto.com

While gathering math ideas for the sisters I'm tutoring, I came across a problem that has a problem. I decided to find out if they could see it too. Here it is:

For the Good Cheer food drive, your class collected 320 cans of food. Each family gets 40 cans of food. How many cartons will you need to pack them?

I'm sure the intended answer is 8 - the number of families who would get food. However, the question asked how many cartons you need. Both girls knew the problem; they needed to know how many cans fit in a carton. We talked about vague, ambiguous, or just plain bad word problems. I told them not to be afraid to speak up when they come across such problems. 

We moved on - 
The bus left the terminal and picked up 5 people at the first stop. At the second stop, 2 people got off and 4 people got on. At the third stop, 3 people got off and 5 got on. How many passengers were now on the bus. 

Instantly, the older girl asked, "Was the bus empty when it left the terminal?" I grinned and congratulated her for getting the message. No test was needed to assess her learning.

That morning, all three of us had a great time playing math!


  1. Nice post Sue. I have encountered several problems like the two you mentioned above, even in reviewed books here in our country.

    I think it's a good exercise to train students spot errors in problems.

  2. Guillermo - Thank you for taking the time to comment on my post. As a college student 5 years ago, I came across several problems with errors on tests for Intro to Chemistry. The teacher was so determined to "explain" things so I could understand, that he never would open his mind to see the errors. If I ever get a classroom of my own, I think I will implement a "3 cheers" program for students who find such errors.