Aptitude - Average - Discussion

@Manoj kumar is it useful for all?

Please give the clear information I'm ok but little confused.

Old School method.

Let Z+65 be weight of 8 person and their average be A.

So, (z+65)/8 = A .......(i).

Now with the replacing the person with 65 KG weight with new person, average becomes A+2.5, let the weight of new person be x KG.

So, (Z+x/8) = A+2.5 .......(ii).

Subtraction (i) from (ii).

(x+65)/8 = 2.5.

Therefor, x = 85.

In this case problems you people just recall this formula:

N - R = (+ or -)nx.

N - new items added.
R - removed items.
n - average of the sum.
x - decrease or increase.

Put + when increase.
- for decrease.

Now see:
N - 65 = + 8(2.5).
N = 85.

Guys it's simple.

Let consider the first case:

The average weight of 8 people be x.
So,
(a+b+c+d+e+f+g+65)/8=x : ( one of the person weighs 65)
=>a+b+c+d+e+f+g+65=8x .........(1).

If the person who weighs 65kg was replaced the average.
i.e. Let the new person weight be Z.

=>(a+b+c+d+e+f+g+Z)/8= x+2.5. :( the average increased by 2.5).
=> (a+b+c+d+e+f+g+Z)=8x+20 ..........(2).

From (1) =>. a+b+c+d+e+f+g+8x= -65 ..........(3).
From(2) =>. a+b+c+d+e+f+g+8x= -z + 20.........(4).

Compare (3) & (4).

-Z+20= -65.
Z= 85 kg.

Is the answer.