Directions: Study the following questions carefully and answer the questions given below.
1

There are 7 friends. If salaries of these friends are in order- 
10K = S1  S2 ≥ S3  ≥ S4 ≥….. ≥ S7 = 5K

Which of the following can’t be the average of these 7 friends.

» Explain it
C
Maximum average could be 

(10 + 10 + 10 + 10 + 10 + 10 + 5)  = 9.28
7

Which is being satisfied by option C i.e.  9.42.

Hence, option (C) is correct.
2
The average age of A and B is 20 years. If A is to be replaced by C, the average would be 19 years. The average age of C and A is 21 years. The ages of A, B and C in order (in years) are
» Explain it
C
A + B = 2 × 20 = 40 yr        

B + C = 2 × 19 = 38 yr

C + A = 2 × 21 = 42 yr

On adding all three,

2 (A + B + C) = 40 + 38 + 42 = 120

⇒ A + B + C = 60

∴    A = (A + B + C) – (B + C) = 60 – 38 = 22 yr

Similarly,

B = (A + B) – A = 40 – 22 = 18 yr

C = (C + A) – A = 42 – 22 = 20 yr

Note: In this question we can save 4-5 seconds by not calculating the age of the third person as with only the respective ages of A and B we can confirm the correct answer out of the given options.

Hence, option (C) is correct.
3
The average monthly income of a family of four earning members was Rs. 15130. One of the daughters in the family got married and left home, so the average monthly income of the family came down to Rs. 14660. What is the monthly income of the married daughter ?
» Explain it
C
Total monthly income of 4 members = 15130 × 4  =  Rs. 60520

Except daughter, total monthly income of 3 members = 14660 × 3  =  Rs. 43980

∴  Monthly income of married daughter = 60520 – 43980  =  Rs. 16540

Hence, option (C) is correct.
4
A man purchases milk for three consecutive years. In the first year, he purchases milk at the rate of Rs. 7.50 per litre, in the second year, at the rate of Rs. 8.00 per litre and in the third year, at Rs. 8.50 per litre. If he purchases milk worth Rs. 4,080 each year, the average price of milk per litre for the three years is
» Explain it
B
Price of milk in first year = Rs. 7.50 per litre.

∴  Quantity of milk in first year =  4080  = 544 litres
7.50

Price of milk in second year = Rs. 8.00 per litre.

∴  Quantity of milk in second year =  4080  = 510 litres
8.00

Price of milk in third year = Rs. 8.50 per litre.

∴  Quantity of milk in third year =  4080  = 480 litres
8.50

∴  Required average =  3 × 4080
544 + 510 + 480

 =  12240   =  Rs. 7.98
1534

Hence, option (B) is correct.
5
The average weight of 21 boys was recorded as 64 kg. If the weight of the teacher was added, the average increased by one kg. What was the teacher's weight ?
» Explain it
A
Total weight of 21 boys = 64 × 21 = 1344 kg

Given that if the weight of the teacher was added, the average increased by one kg

∴  Total weight along with the teacher = 65 × 22 = 1430 kg

Now,  teacher's weight = 1430 – 1344 = 86

Hence, option (A) is correct.