Aptitude - Average - Discussion

Why we need to subtract 6250? I can hardly understand.

5050+5200+6250 = 16500 Now Q and R is 6250 i.e 2*6250 = 12500.

Now P is 16500-12500 = 4000.

P and Q is Rs. 5050.
P and R is Rs. 5200.
Q and R is Rs. 6250.

5050+5200-6250 = 4000.

If the average income of 10 persons is Rs. 21 and the average income of 150 persons is Rs. 25. Then find the average income of 50 persons.

Let p&q =5050---(1).
q& r = 6250 --- (2).
p&r = 5200---(3).

We have to find p?
So, (1)+(3)p&q+p&r = 5050+5200.

p&Q&r = 10250 already given q&r = 6250.

We need to find p only, so p = (p&Q&r)10250 -(q&r)6250 (1)+(3)-(2).

p = 4000.

P and Q = 5050.
Q and R = 6250.
P and R = 5200.

We need income of p.

So 6250-5050 = 1200.

5200 - 1200.

= 4000.

Hi @Swathi, the answer for your question is 47.5 minutes.

How means,
For 5 minutes secret can be told to 2 people,
In the next 5 minutes 2 people can told to another 2 people each so total 4 in second 5 minutes.
3rd 5 minutes 8.
4th 5 minutes 16.
.........
.........
9th 5 minutes 512.

Now the completed minutes are 9*5=45 minutes and secret reached to 512 persons.

In the next 5 minutes it can reach to 1024 people but we don't have 1024 people, we have only 768 people..so the people who didn't get the secret till now are 256.

So within 2.5 minutes if the persons in (512/2) told secret to one person each, then the secret will be reaching to 768 people in 45+2.5 = 47.5 minutes.

6250-5050 = 1200.
5200-1200 = 4000.

p/2+q/2 = 5050-------1.
q/2+r/2 = 6250--------2.

from equation 2,
q/2 = 6250-r/2.

Put equation 1 in q/2.

p/2+6250-r/2 = 5050.
p/2-r/2 = 5050-6250.
p/2-r/2 = -1200.

According 3 condition,

p/2+r/2 = 5200-------3.

From add 2 and 3,

p/2-r/2+p/2+r/2 = -1200+500.

p/2+p/2 = 4000.
p = 4000.

@Praveen how did you get -(q+r) can you explain in detail?