Answer:
19.3333333
Step-by-step explanation:
You make an improper fraction and multiply
By definition, the number
is the ratio between the circumference and the diameter:

This implies that

And so your circumference is 
Answer: Yes it is reasonable.
Step-by-step explanation:
If all the numbers are rounded, 79 will be rounded to 80
12 to 10
and 11 to 10
If there are about 80 kids in 3rd grade, and about 20 kids in Mrs. Henry's class (because 10 girls plus 10 boys)
That means that 80-20
about 60 kids are not in Mrs. Henry's class
Hope this helped!