Answer keys for test are posted when the tests are returned. Each solution key provides the correct answer, and, for some of the more conceptual questions, a short discussion of the answer.
Click on the link to view and download each answer key. Answer keys are formatted as HTML files.

Test 1   Answer Keys:     Version 1     Version 2     Version 3
Test 2   Answer Keys:     Version 1     Version 2     Version 3
Test 3   Answer Keys:     Version 1     Version 2     Version 3
Test 4   Answer Keys:     Version 1     Version 2     Version 3

EXAM	MEAN	RANGE	NUMBER
Test 1	127.4	204 - 60	135
Test 2	126.8	198 - 42	125
Test 3	123.2	192 - 54	122
Test 4	123.4	174 - 24	119
Final

Running cumulative class average after Test 4   =   500.8   (63 %)
Highest cumulative score   =   714  

Please be aware of two facets of this course which will cause the class average to change during the semester.
(1)   When students drop the course, their scores are deleted, and no longer counted in the averages. Only scores for students who complete the course are counted towards the class average. Since people often drop the class because of low test scores, this has the effect of raising the averages for the first two tests (which occur before the drop deadline).
(2)   The average quoted above is based on 4 test scores. A substantial number of students will opt to drop one score, their lowest score. Their good scores will be weighted more, resulting in an overall class average at the end of the semester, that will be larger than the average after Test 4, which is the last average quoted before the final.

Estimating your current course letter grade:

Here's how to determine your grade status in this class:
(1)   Total up your test scores.
(2)   Each exam is worth 200 points. Divide your current cumulative score by the number of tests times 200. You will get a fraction between 0 and 1.
(3)   Multiply this fraction by 100. Your current class score is now expressed as a percent, from 0 to 100%.
(4)   Compare your percent to the grade scale given in the syllabus.

As stated in the course syllabus, an adjustment to this scale may be made at the end of the semester, to reflect the overall class performance. Based on previous experience with astronomy survey classes, the usual adjustment is to drop the lower value for each letter grade by a few percentage points.

Since the final letter grades will reflect the class performance, a good way to estimate your letter grade is to compare your cumulative test score with the class average, given above.

The class average is defined to be the border between a B and a C.

If your total is substantially better than the class average, you have an A.
If your total is somewhat better than the class average, you have a B.
If your total is somewhat lower than the class average, you have a C.
If your total is substantially worse than the class average, you have an D.
If your total is less than 50%, you are in danger of failing the class.

Option II - Dropping the low test score

You may drop your lowest test score, in order to improve your final grade. This action is optional. If you choose to drop your lowest test, you must indicate this choice in the appropriate place on the final exam cover sheet. Students who completely missed a test will have that score dropped automatically.

How does this work ?

If you choose to drop your lowest test score, then....

• Each test AND the final exam will count for 250 points.
• Total your 3 best test scores. Multiply the total by 1.25 (= 250/200). This accounts for the fact that each of the hourly exams now counts for a larger percentage of your total score.
• Divide this total by 750 (the sum of 3, 250 point tests). The result is the same fraction as described above. After multiplying this fraction by 100, to convert to a percent, you can compare your score to the grade scale posted in the syllabus.
• Compare your revised total (after multiplication), to the class average.
• Estimate your current letter grade as described above.

An example:   Suppose your four test scores were: 128, 150, 95, 126. Dropping the low score here is a no-brainer. Totaling the remaining three scores = 404. Multiplying by 1.25 gives a cumulative score = 505. This corresponds to a percentage of 67.3% (= 505/750).   If you did not drop a score, the percentage would be 499/800 = 62.4%   In this case, that might be the difference between a C and a D letter grade.

Should I drop ?

• If you have one low test score, compared to the other three scores, your chances of improving your final grade are good; so its probably best to drop the low score.
• If your scores are all about the same, or you have two high and two low scores, its best not to drop a test score.
• Remember that if you drop a score, you are assuming that you will perform better on the final, compared to the dropped test score.