# Average

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Hello sir, Can you please explain this question

Rajiv is a student in a business school. After every test he calculates his cumulative average. QT and OB were his last two tests. 83 marks in QT increased his average by 2. 75 marks in OB further increased his average by 1. Reasoning is the next test, if he gets 51 in Reasoning, his average will be _____?

1. 63
2. 62
3. 61
4. 60

Hello Ritika,

Find the solution.........

Let initial average =a and number of subjects = n

According to first condition,

an + 83 = (n+1) (a + 2)

an + 83 = an + 2n + a + 2

a + 2n = 81…………………1)

According to second condition,

{(a + 2) (n + 1)+ 75} = (a+2+1)(n+2)

an + a +2n + 2 + 75 = an + 2a + 3n + 6

a + n =71 …………………………..2)

From eq. 1) and 2)

n = 10 and x = 61

After paper OT and OB

Average = 61 + 2 + 1 =64

Number of subjects = 10 + 1 + 1 =12

So after getting 51 in reasoning,

Average = (64 x 12 + 51)/(13) =819/13=63

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In a house ABC with 12 members, the avg age of the members was 42 years in the year 1966. The next year, the oldest member of the family died at the age of 66 and a member decided to shift to other locality. After 1 year a baby was born and in the same year another member left the house who is 3 years younger to the member who had left the house the previous year. After 2 more years, the average age of all the members was 44 years. What was the age of the member who had left the house when the oldest member died?

A. 20 B.21 C. 41 D.42

This post was modified 7 months ago by Gaurav Jain
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A few students decided to buy a gift for their teacher. So, each of them decided to contribute an equal amount for the gift. But when they went to buy the gift, they found that the price of it had increased by 16.66%. Now 2 more students joined to contribute and because of this the cost per head decreased by Re 1. If the contribution per head is an integer, which of the following cant be the initial number of students who had decided to contribute for the gift?

A. 5    B.6    C. 7    D.8

initial contribution p , and number = n , so initial price = pn

and final price = 7/6pn

final contri = p-1 and number of students = n+2

so 7/6pn = (p-1) (n+2)

from this n = (12p-12)/(p+6)

now n=7 won't be possible

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