7. (10 points) 30 tigers and 30 foxes are divided into 20 groups, with 3 animals in each group. Tigers always tell the truth, while foxes always lie. When asked if there are any foxes in the group, 39 out of the 60 animals answered “no”. How many groups consist of 3 tigers? 

Groups.
3
【Answer】Solution: According to the analysis, since there are 30 foxes, and they all lie, when asked "Is there a fox in the group?", they will definitely all say "No", so the foxes saying "No" total 30 times. The tigers tell the truth, so in a group where there are foxes, the tigers will say "Yes", and only when all 3 animals are tigers will they say "No".
Therefore, when 3 tigers are in the same group, there will be 3 voices saying "No". Hence, the number of groups where all 3 animals are tigers is: $(39-30) \div 3=9 \div 3=3$ (groups).
The answer is: 3.