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Two students A and B participate in Physics and Chemistry exams. Each exam subject has 6 different exam codes and two exam subjects have their own different exam codes. In each exam subject, each student receives randomly exam code. What is the probability that A and B receive the same exam code in only one subject?

A. 7/18
B. 4/9
C. 2/9
D. 5/18
E. 1/36


Are You Up For the Challenge: 700 Level Questions

Let’s say the first student already has two codes: one for Physics and the other for Chemistry. The second student has ⅙ chance to match the same code in Physics as the first student and ⅚ chance not to match the same code Chemistry. Therefore, the second student has ⅙ x ⅚ = 5/36 chance to have the same code in Physics but not in Chemistry. Using the same logic, we can see that he will also has 5/36 chance to have the same code in Chemistry but not in Physics. Therefore, the probability is 5/36 + 5/56 = 10/36 = 5/18.

Answer: D
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Got this one quickly by recognising P (Same in one) = 1 - P (Same in both or neither)

P (same in both) = 1/6 * 1/6 = 1/36
P (same in neither) = 5/6 * 5/6 = 25/36

therefore P (Both OR Neither) = 26/36
1 - 26/36 = 10/36 = 5/18

Option D is correct.
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