I don't really know if this is correct but I think it is x+y+z=14
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.
Answer To change a fraction into an equivalent fraction with a denominator of 100: 1. establish how many times the given denominator fits (divides) into 100 2. multiply both the numerator and the denominator by that number. Remember that factor pairs of 100 could be of assistance.
Step-by-step explanation:
Answer:
9/17
Step-by-step explanation:
there are 17 marbles in total 9 of them are blue therefore, 9/17 is the correct answer