Aptitude - Average - Discussion

Thanks for your support guys. Will post more useful information in future.

@Manoj Kumar Sir, your tricks are really useful.

I am totally confused. Can any one give me solution?

The first line says average weight weight of person is increased by 2.5.

1) So the total weight increase is = 2.5*8 = 20.

2) Then it says when old person weighting 65 kg is replaced by new one since the weight increase is because of only one person add the old person weight+the average weight = 65+20 = 85.

Let average of 8 person weight = x;

x/8 = 2.5;
x = 8*2.5.
x = 20;

New person is add with weight = 65.

65+20 = 85.
Ans = 85;

Weight of newly came person is = Weight of replaced person + (no of persons*increased in weight).

=>65+ (8*2.5).

=>65+20.

=>85.

@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.

Dear Friends.

Try this one below. There are only the following three cases possible if a group is disturbed.

Case 1: If a person is replaced by another one (Note: Here number of persons in the group remains same after replacement).

Case 2: If a person joins the existing group (Note: Here number of persons in the group will get increased by 1 after joining of a new one).

Case 3: If a person leaves from existing group (Note: Here number of persons in the group will get decreased by 1 after removal of old one).

Formula for Case 1:

1. If average weight is increased, then.

Weight of new comer = Weight of the person left + (No. of persons X Increase in average weight).

2. If average weight is decreased then.

Weight of new comer = Weight of the person left - (No. of persons X Decrease in average weight).

Formula for Case 2:

1. If average weight is increased then.

Weight of new comer = Previous average weight + (No. of persons including new comer X Increase in average weight).

2. If average weight is decreased then.

Weight of new comer = Previous average weight - (No. of persons including new comer X Decrease in average weight).

Formula for Case 3:

1. If average weight is increased then.

Weight of person left = Previous average weight + (No. of persons excluding the person left X Increase in average weight).

2. If average weight is decreased then.

Weight of person left = Previous average weight - (No. of persons excluding the person left X Decrease in average weight).

The above formulas can also be used for calculating age instead of weight & can be used for other things instead of persons.

Hope this was useful.