Aptitude - Average - Discussion

@Neha and @Pratiksha.

Average = sum of the given no /total no.

In the given question you have given the average of 2 grandparents, 2parents and 3 grandchildren. Now you have to calculate the average of all family members.

From the average, we can calculate sum of the numbers as;

Average = sum of the given number/total number.
Sum of the given numbers =avg * total number.

Total number = sum of the given number/avg.

From above data, we can calculate sum of numbers

Avg of 2 grandparents = 67.
Total no grandparents = 2.
Sum of the ages of grandparents = ?

According to formula,
Avg = sum of total no/total no.
Sum of total no = avg * total no.
Sum of total no = 67 * 2 = 134.

Sum of ages of two grandparents is 134 likewise,
Sum of 2 parents is = 35 * 2 = 70.
Sum of three grandchildren is = 6 * 3 = 18.

Now we have to calculate all average of the family.
Total no of family members are 7 i.e. 2 grandparent ,2parents, 3grandchildren
2 + 2 + 3 = .

Avg of total family members = sum of the ages of family members/total no of family members.

As we count sum of ages all family members,
(134 + 70 + 18)/7 = 222/7 = 31.6 = 31 5/7.

Why can't we consider the chidren as 2 memebers and do the average?

Why is 31 5/7 is come?
Let's divide 31 by 7.

The answer is : Here the remainder 31 and the quotient is 5. So 31.5 and we need to mention the number of members so 7.
That's why the answer is 31.5/7.

Required average = 67 x 2 + 35 x 2 + 6 x 3.
-----------------------
2 + 2 + 3
= 134 + 70 + 18
---------------
7
= 222
-----
7
= 31 5 years.
-
7

Divide:

7)222(31
- 21
-------
12
- 7
-------
5
-------
so that is right it like 31 5
--------------------------
7

How comes 5/7 I got 31.7142?

Please explain, why for parents also your multiplying by 2 and for two grandparents also multiplying by 2. Why can't we consider like this.

For parents means = Father and mother, hence its multiplied by 2.

For 2 grandparents means = Father's father, father's mother, mother'father, mothers mother, hence it should be 4.

Please some one reply am I right or wrong, if no please explain.

Can someone crack such problems with some other approach, shortcut maybe?

Why 222 would became 315? Can someone please explain me?

Family = Two grand parents = 2*67 = 134, two parents = 2*35 = 70, three grand children = 3*6 = 18.

After started in 134+70+18. Total members: 222/7 = 31.5/7.

It's a wrong method already average of ages were given how can we count them as 7 members.