Here are several types of confusion I see students sometimes having on Part 2 of the word problem where you are asked to write an equation.
- Make sure to you write an equation. Take for example the following problem.
Anna, Lea, and Simon have ages that add up to be 78. If they were all born in consecutive years, how old is each one?
Occasionally, I'll get an answer like.... x + (x+1) + (x+2). Now this is a good start, but that is just an expression.
- Make sure you have more than words in your equation. The word equation is a great tool for getting an equation but it isn't the equation. Take the same word problem.
Anna, Lea, and Simon have ages that add up to be 78. If they were all born in consecutive years, how old is each one?
Anna + Lea + Simon = 78 or the youngest+the middle child+the oldest = 78
is a good start, but the equation that would get you credit on part 2 would be something like x + (x+1) + (x+2) = 78
- The formula is the frame, but I want the picture. It sometimes happens when students are working a problem that involves a formula that the student will simply write the formula for part 2. Take for example...
The perimeter of is 108. If the length of a rectangle is twice the width, what are the dimensions?
Sometimes a student writes 2w+2l=p or 2w+2l=108. A credit worthy answer would be something like 2w + 2(2w) = 108
- Make sure your number of equations and number of variables match. I kind of lied in the last bullet saying that 2w+2l=108 couldn't be a correct answer. It could be part of a correct answer. By itself there are two different variables in only one equation. You cannot get a single solution for that equation, only a series of solution pairs. However, if you coupled it with another equation in the same two variables then you would get full credit because your number of equations and number of variables now match. Remember the length is twice the width, so I can write l=2w. Together those two equations would get full credit for part 2.
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