Given : - Square ABCD with side 3. E and F as midpoints.
To find : - area of EBFD
Solution : - We have, area of square ABCD = 3 x 3 = 9 units.
Thus, (ar)EBFD = ar ABCD - ar DAE - arDCF
arDAE = 1/2 x base x height
=1/2 x 1.5 x 3 ( AE is 1/2 of AB = 1.5, DA is altitude)
= 2.25
arDFC = 1/2 x base x height
= 1/2 x 1.5 x 3 (FC is 1/2 of BC, DC is altitude)
= 2.25
Thus, (ar) EBFD = arABCD - arDAE - arDCF
= 9 - 2.25 - 2.25
= 4.5 units.
Thus, area of quad EBFD is 4.5 units.
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.