Answer:
I think the answer for the first one is 3 I am not sure about the second one
Answer:

Step-by-step explanation:
Since there are 20 students, this will be the denominator.
Now, to find how many students have a dog and a cat, you need to subtract all the numbers with 20. The leftover number will be the amount of students.
7+8+8=23
23-20=3
So, there are 3 students who have a dog and a cat.
So, the fraction will be 
That does not make sense sorry :(
Answer:
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If the signs of the rational numbers are the same, you add them, i.e. ++ or --.
If they are different, you subtract them, i.e. +- or -+