T&Q: Calculated question rounding error for answer key

The Answer key can display an incorrect value due to a rounding error for an edge case like the following.

For example, suppose a very precise and correct answer for a formula is “2.6454798891706”. Now suppose the formula is configured to display 3 decimal places for the correct answer. The answer key currently presents the correct answer with a rounding error.

• Currently: The answer key displays as 2.646.

• Expected: The answer key should display as 2.645.

This rounding error happens because SamigoExpressionParser.parse returns the string “2.6455” as the answer, which is rounded again downstream (by some client code) to 2.646. These kinds of rounding errors could be prevented by modifying the parse method to return a string with an extra decimal place of precision (e.g., “2.6548” would be rounded to the expected “2.645”).

For what it’s worth, I encountered this problem by testing the following trigonometry example from the T&Q help document, How do I create a calculated question? 

Solve: COS({a}) * ({c} - {b}) = {{z}}

A student’s case arose where variable values resulted in:

COS(4.087) * (3.652 - 8.171)

Using a scientific calculator --with angles set to radians (instead of degrees)-- I discovered that a precise answer like 2.6454798891706 would be presented in the answer key as 2.646 instead of 2.645 (with the default setting of 3 decimal places).