Answer:
Here is a Venn diagram that represents the given:
F B
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\ /
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/ \
/ \
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G B
In this diagram, F represents the set of students who study French, G represents the set of students who study German, and B represents the set of students who study both French and German.
The information given tells us that 13 students study French, 5 study only German, and 6 study both French and German. Therefore, we can place 13 in the region for F, 5 in the region for G, and 6 in the overlapping region for B. The total number of students is 18, so we can calculate the number of students who study only French as 13 - 6 = 7, and the number of students who study only German as 5 - 6 = -1 (which doesn't make sense in this context, so we can ignore it).