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I entered the correct math expression, why did I get the problem wrong?

When working on math exercises that involve entering an expression, students sometimes report that they cannot enter a correct expression, even though it's the answer shown in the hints. (We assume they'll look through the hints when an answer is unknown or marked as incorrect.) There are three ways such a problem might arise.

  1. The answer entered isn't really the same as the answer in the hints.
  2. It isn't obvious how to enter the answer in the hints. The appearance of square brackets, [], is the most common cause of this instance of the problem.
  3. The answer in the hints is incorrect.

As an example of the first case, a hint might show that the correct answer is

 

but, when the user enters "1/2p", the answer is marked as incorrect. What's up?

The answer is "order of operations". Remember PEMDAS? The expression as entered is equivalent to "1/2×p". So it will evaluate "1/2", then multiply the result by "p".  "1/2" times "p" is the same as "p/2". That is not at all the same as the correct answer, specified in the hints.

To fix this, use parentheses! If you enter "1/(2p)", the evaluator has no choice but to use "2p" as the denominator, as shown in the hint. Use parentheses to show the evaluator which part of the problem to evaluate first. 

 

 

 

The second case involves the use of brackets. For example, a hint may display the correct answer with brackets (shown below).

However, if you try to enter the answer with brackets, the problem says there are more parts to the problem. Simply replace the brackets with parentheses and your answer will be accepted. 

 

 

The 3rd kind of situation means there is an error with the hints/problem itself. In this case, please follow the instructions in this article. 

 

September 7 2016

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