Aptitude - Average - Discussion

Simple formula.

Weight Of replcae +- (increase/decrease)* number.

Let the average was 10.

Then the sum of 8 people was 10*8 = 80.
When new person comes ,average was increased by 2.5 so new average is 12.5 the new sum = 12.5 * 8 = 100.

So the difference is of 20.
Now whoever new person he will increase the sum by 20 so new person weight is 65 + 20 =85 is the Answer.

By using formula,
a = r+nx ------>
a = Added value.
r = Removed value.
n = Number of persons.
x = Change in avg.

So,
a = 65+8(2.5).
a = 85 is new person weight.

Let's suppose Average age = 10
Age of sum of 8 ppl = 8×10 = 80
If age increases by 2.5 then = 12.5×8= 100,
Difference= 100-80 = 20.
New person age plus the difference of the ages of the first 8 ppl = 65+20,
= 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.

Average = Weights /number of members.

So,
Weights = Average * number of members.

If the Average increased by 2.5, then:
Weights will increase by (2.5 * 8) = 20.

Increase in weights = 20 kg,
The new person's weight = 65 + 20 = 85 kg.

2.5 = 2 + 1/2 = 5/2
8 × 5/2 = 20,
65 + 20 = 85.

Not able to understand.

Here you poised 20kg to this person's weight but not well 20kg should be added to all persons in one person's weight only 2.5kg should be added.

Am I right.

Let x be an average of 8 persons.
Let y be the weight of the new person.
(x+y-65)/8 = (x/8)+2.5,
x+y-65 = x+20,
y-65 = 20,
y = 85.

Hai @Likha,

The question is very clear. it says. a person of 65 kg left and a new comer joined.
Average = (total sum of the scores) divided by No. of scores.
Sum of all persons (including 65 kg weighing person)/8 = X(average).
Sum of weight of 7 persons = 8X - 65 ------------------(1)
When joined another who weighs N, average increased by 2.5 kg
ie (sum of 7 person's weight + N) / 8 = X +2.5,
From (1) we get (8X - 65 + N) / 8 = X + 2.5,
8X - 65 + N = 8 *(X+ 2.5),
8X - 65 + N = 8X + 20,
N = 8X + 20 - 8X + 65,
N = 20 + 65,
N = 85.

The weight of new comer is 85 kg. the answer