Answer:
I BELIEVE ITS C
Step-by-step explanation:
A&d i think.. but basically the equation needs to be modeled where the answer will be a 14° difference
Answer: The average was 9 years old find the average age of both groups is 10 years old.
Step-by-step explanation:
Formula foe average : 
Given : The first group of students consists of 10 and their average age was 13 years old.
i.e.
(1)
The next group consisted of 30 students and their average was 9 years old.
i.e.
(2)
Then from (1) and (2) , the sum of both groups (first group and next group )students = 130+270 =400
Combined students of both groups (first and next group )= 10+30=40
Now , the average of both groups =

Hence, the average was 9 years old find the average age of both groups is 10 years old.
11/15-2/5
Multiply 2 and 5 to get a common denominator of 15
11/15-6/15
=4/15