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: $2.40
Step-by-step explanation:
$7.20 divided by 3.
Answer:
a = 4
Step-by-step explanation:
a + 2 = 6
Subtract 2 from both sides
a + 2 - 2 = 6 - 2
a = 4
1/2 x 5/8 = .3125
If you plug it into the calculator.