PrairieLearn tips

Inputting answers

• No Fractions: Do not use fractions as your input answer. Instead use decimal numbers (e.g. 2/3 is not accepted as a correct answer, however 0.667 is).
• Error tolerance is 1%: Your answer must be accurate to within a relative tolerance of 0.01.

  • For example, you may (correctly) compute a strain value of x = 1.17*10^(-3) using symbolic expressions. If you enter your answer as x = 0.0012 (exactly five digits, and two significant digits), PrairieLearn will mark the answer 0.0012 incorrect, as the difference between these two values is about 2.5% (that is, (1.2-1.17)/1.17 = 0.0256) and exceeds PL's tolerance for correct answers.

• Parenthesis: You should be obsessive about making sure your equations are typed correctly.
  • Example: Powers - the entire base is wrapped in parenthesis as well as the power (i.e. 3*2^1/3 vs. (3*2)^(1/3)).
  • Example: Division - the numerator and denominator are both individually wrapped in parenthesis (i.e. 1/2*3 vs. 1/(2*3)).
  • Your code should look like you don't trust the built-in order of operations. Be obsessive.
• Units: It is your responsibility to check the units in your problem.
  • You should know the base units (i.e. \( \rm\ MPa = \frac{\rm N}{\rm mm^2} \) , \( \rm\ ksi = \frac{\rm kips}{\rm in^2} \) , etc.) and how to convert given units (i.e. \( \rm\ MPa = 10^6 \ Pa, 12 \ \text{in} = 1 \ \text{ft} \) , etc.). This is another thing that you should be very careful about. When doing a problem, it is good to write out the units as a separate equation to make sure that it makes sense. For example:
    $$ \begin{align} \delta &= \frac{FL}{EA} \\ [\rm mm] &= \frac{[\rm kN][\rm mm]}{[\rm MPa][\rm mm^2]} \\ [\rm mm] &= \frac{[\rm kN][\rm mm]}{[\frac{\rm N}{\rm mm^2}][\rm mm^2]} = \frac{[10^3 \rm N][\rm mm^3]}{[\rm N][\rm mm^2]} \\ \therefore [\rm mm] &= [\rm mm] \end{align} $$
    Note: The \(10^3\) conversion would need to be applied to the force for the final equation to be true.
  • If everything is given in \(\rm\ N\) and \(\rm\ m\), but the answers ask for \(\rm\ kN\) and \(\rm\ mm\), then it is your responsibility to convert the answer. Be obsessive about checking these things before submitting your answer.

Reviewing for CBTF Quizzes

Review for quizzes with the relevant homework assignment. The course website tells you which homeworks are relevant and explicitly states the topics covered in each quiz. The quiz problems are similar to those found on the homework.

Doing the homework, it’s important to make sure that you fully understand as completely as possible the solution you reach for each question. When reviewing your homework problems, you should make sure that you can do the problem on paper, type it into your calculator of choice, and get the correct answer on the first try. It’s easy to overlook some key concepts in the course by “brute forcing” signs and units in the homework (see above). If you find you are consistently getting answers off by factors of 10, or making a sign error, it can be easy to correct and overlook while doing the homework, but be very costly during the quiz.

If you are arriving at the correct answer on your first try for each of the homework questions, then the next step would be to consider potential modifications to the questions. How would the procedure for solving the problem change if you were given different information? What information was absolutely necessary to solve the problem? Do you understand why you were able to make all of the assumptions you did?

Using a Python script is strongly recommended as is can help you keep track of your work.

Computer Based Testing Facility (CBTF)

If you are not familiar with taking computer based tests at UIUC, we strongly recommend

• Watching this video
• Reviewing the policies and procedures on their website.
• Reviewing this orientation

Important CBTF Policies

• If you have any problem during the exam, raise your hand. A proctor will come and help you. Remember that proctors cannot answer questions specific to your test. Use your best judgement.
• If you missed an exam for whatever reason, you can go see a proctor at the CBTF in person. They will help you sign up for another exam.
• For more information, check out the FAQ page.

Computation at CBTF

• Personal calculators are not allowed in the CBTF. You can use calculators supplied by the CBTF, or Python that is available within PrairieLearn.
• Degrees vs. Radians: Make sure that you know how the computational tool you are using calculates cos and sin. If you want to check this, you can calculate a quantity like \(\cos(90)\) which should equal \(0\) .
• CBTF calculator cheat sheet and calculator video tutorial