Aptitude - Average - Discussion

The new average is increased by 2.5, so we can say 8 * 2.5 = 20kg is the newly increased weight.

Such that the old person weight is 65 kg.

We have the newly added person weight, so 65 + 20 = 85 kg.

Here;
2 +1/2 Means 5/2.
a = 65+8* 5/2.
a = 85 is the new person's weight.

Age of captain = 26 ...
So the age of the wicket-keeper who is 3 years older than the captain = 29
Let avg of 11 members be x, then
The sum of observations /11 = x.

I. e 26+29+ remaining sum of 9 members = 11x.
Remaining sum of 9 = 11x-55--->(1)
Given that, avg of the remaining 9 will be one less than the total average.
So total avg is x, then the of 9 is x-1.

I. e sum of remaining 9/9 = x-1.
Sum of remaining 9 = 9x-9 ----> (2)
9x-9 = 11x-55 from 1 and 2.

11x -9x = -9+55.
2x = 46,
x= 46/2 = 23.

Let as assume A is average,
x is new person.
8A - 65 +x = 8*(A+2.5)
x = 85.

The average weight of 8 person's increases by 2.5 kg.

Assume 8 persons.
a, b, c, d, e, f , g, h then,

(a + b + c + d + e + f + g + h)/8 = x + 2.5
(a + b + c + d + e + f + g + h = 8 ( x + 2.5)
= 8x + 20 -----------> 1

When a new person comes in place of one of them weighing 65 kg
then

(a + b + c + d + e + f + g + h + 65)/9 = x
(a + b + c + d + e + f + g + h + 65) = 9 x
(a + b + c + d + e + f + g + h= 9x - 65 -------------> 2

Solving eguation1 and 2

8x + 20 = 9x - 65.
20 + 65 = 9x - 8x.
85 = x.

Total weight of 8 persons is 520 (65*8).
Now, a total weight of 7 persons is 455 (520-65),
Now try every option to get 2.5% increase,
(455+85)/8 is equal to 67.5,
The total increase is 2.5 KG (67.5-65),
Ans is 85 KG.

Can you guys tell me about what happens if the weight is decreased by 2.5 kg? Please explain.

Hai Friends.

Try this method.

New person weight =Replaced person weight+ (no. Of persons*increased weight).

Replaced person weight =65.

No. Of persons =8.

Increased weight =2.5.

These all values are replaced in the formula, then we get the answer "85".

There is very simple formula for this.

Weight of New person = No of Persons * Increased weight + Replaced.

So, 8 * 2.5 + 65 = 85.

Thank you @All, for the explanation.