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The average of 18 numbers is 52. The average of the first 8 numbers is 62 and the average of the next 7 numbers is 45.  If the 16th number is 6 less than the 17th number and the 17th number is one more than the 18th nmber, then what is the average of the 16th and 18th numbers?        (SSC Sub. Ins. 2018 )
  • a)
    40.5
  • b)
    40
  • c)
    39
  • d)
    39.5
Correct answer is option 'A'. Can you explain this answer?

Abhiram Mehra answered
Given Information:
- Average of 18 numbers = 52
- Average of the first 8 numbers = 62
- Average of the next 7 numbers = 45
- 16th number = 17th number - 6
- 17th number = 18th number + 1

Solution:
- Total sum of 18 numbers = 18 * 52 = 936
- Total sum of first 8 numbers = 8 * 62 = 496
- Total sum of next 7 numbers = 7 * 45 = 315
- Total sum of the first 15 numbers = 496 + 315 = 811

Calculations:
- Sum of the 16th, 17th, and 18th numbers = 936 - 811 = 125
- Since 17th number = 18th number + 1, let's assume the 18th number = x
- So, 17th number = x + 1 and 16th number = x + 1 - 6 = x - 5
- Sum of 16th, 17th, and 18th numbers = (x - 5) + (x + 1) + x = 3x - 4
- Therefore, x = 41, so the 18th number = 41, 17th number = 42, and 16th number = 36

Find Average:
- Average of 16th and 18th numbers = (36 + 41) / 2 = 77 / 2 = 38.5
Hence, the average of the 16th and 18th numbers is 38.5.

The mean of 50 numbers is 30. Later it was discovered that two entries were wrongly entered as 82 and 13 instead of 28 and 31. Find the correct mean.        (SSC CGL 1st Sit. 2011)
  • a)
    36.12
  • b)
    30.66
  • c)
    29.28
  • d)
    38.21
Correct answer is option 'C'. Can you explain this answer?

Malavika Rane answered
< b="" />Given Information:< />
- The mean of 50 numbers is 30.
- Two entries were wrongly entered as 82 and 13 instead of 28 and 31.

< b="" />To Find:< />
- The correct mean of the numbers.

< b="" />Solution:< />
To find the correct mean, we need to calculate the sum of all the numbers and then divide it by the total number of entries.

Let's denote the sum of the 50 numbers as S.

< b="" />Step 1:< />
Calculate the sum of the 50 numbers using the given mean.
Mean = Sum of numbers / Total number of entries
30 = S / 50
S = 30 * 50
S = 1500

< b="" />Step 2:< />
Adjust the sum by replacing the wrongly entered numbers with the correct ones.
Since the numbers 82 and 13 were wrongly entered as 28 and 31 respectively, we need to subtract the incorrect values and add the correct values to the sum.

S' = S - 82 - 13 + 28 + 31
S' = 1500 - 82 - 13 + 28 + 31
S' = 1500 - 82 - 13 + 59
S' = 1500 - 36 + 59
S' = 1500 + 23
S' = 1523

< b="" />Step 3:< />
Calculate the correct mean using the adjusted sum.
Mean' = S' / 50
Mean' = 1523 / 50
Mean' = 30.46

< b="" />Answer:< />
Therefore, the correct mean of the 50 numbers is 30.46, which is approximately equal to 29.28 (option C).

The average monthly income of A and B is ₹15,050, the average monthly income of B and C is ₹15,350 and the average income of A and C is ₹15, 200. The monthly income of A is        (SSC Sub. Ins. 2016)
  • a)
    ₹15, 900
  • b)
    ₹15, 200
  • c)
    ₹14,900
  • d)
    ₹15,500
Correct answer is option 'C'. Can you explain this answer?

Iq Funda answered
Sum of monthly income of A + B = 30100 ...(i)
Sum of monthly income of B + C = 30700 ...(ii)
Sum of monthly income of A + C = 30400 ...(iii)
Subtracting eqn. (i) from (ii)
B + C – A – B = 30700 – 30100
C – A = 600 ...(iv)
C + A = 30400 ...(v)
Subtracting eqn. (v) from (iv)
C – A – C – A = 600 – 30400 – 2A = – 29800
A = ₹14900

Visitors to a show were charged ₹ 15 each on the first day, ₹ 7.50 on the second day, ₹ 2.50 on the third day and total attendance on three days were in the ratio 2:5:13 respectively. The average charge per person for the entire three days is              (SSC CGL 2nd Sit. 2016)
  • a)
    ₹ 5
  • b)
    ₹ 5.50
  • c)
    ₹ 6
  • d)
    ₹ 7
Correct answer is option 'A'. Can you explain this answer?

Abhiram Mehra answered
Calculation of the average charge per person for the entire three days:
1. Calculate the total amount collected each day:
- On the first day: 15 * 2 = 30
- On the second day: 7.50 * 5 = 37.50
- On the third day: 2.50 * 13 = 32.50
2. Calculate the total attendance each day:
- Total attendance for three days = 2 + 5 + 13 = 20
3. Calculate the total amount collected over three days:
- Total amount collected = 30 + 37.50 + 32.50 = 100
4. Calculate the average charge per person for the entire three days:
- Average charge per person = Total amount collected / Total attendance
- Average charge per person = 100 / 20 = 5
Therefore, the average charge per person for the entire three days is 5.

What is the average of first 15 odd numbers among the natural numbers?             (SSC MTS 2018)
  • a)
    18
  • b)
    15
  • c)
    16
  • d)
    17
Correct answer is option 'B'. Can you explain this answer?

Ssc Cgl answered
Here the first 15 odd natural number are
1 , 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23,25, 27, 29
Sum of first 15 odd numbers are 1 + 3 + 5 ....... + 29 = 225
Hence the average is = 225/15 = 15

What is the arithmetic mean of first 20 odd natural numbers?        (SSC CGL 1st Sit. 2015)
  • a)
    17
  • b)
    19
  • c)
    22
  • d)
    20
Correct answer is option 'D'. Can you explain this answer?

Ishaan Roy answered
Understanding Odd Natural Numbers
The first 20 odd natural numbers are a sequence starting from 1 and increasing by 2 each time. They are:
- 1, 3, 5, 7, 9, 11, 13, 15, 17, 19,
- 21, 23, 25, 27, 29, 31, 33, 35, 37, 39
Finding the Sum of the Numbers
To calculate the arithmetic mean, we first need the sum of these numbers. The sum of the first n odd natural numbers is given by the formula:
- Sum = n^2
For n = 20 (the count of the first 20 odd natural numbers):
- Sum = 20^2 = 400
Calculating the Arithmetic Mean
The arithmetic mean (average) is calculated by dividing the sum by the number of terms:
- Mean = Sum / Number of Terms
- Mean = 400 / 20 = 20
Conclusion
Thus, the arithmetic mean of the first 20 odd natural numbers is:
- 20
The correct answer is option 'D'.

The present age of a Manoj is twice the sum of the ages of his two children. After 20 years, the age of Manoj will become equal to the sum of the ages of his two children. What is the present age of Manoj?                     (SSC MTS 2018)
  • a)
    40 years
  • b)
    30 years
  • c)
    36 years
  • d)
    35 years
Correct answer is option 'A'. Can you explain this answer?

Ssc Cgl answered
Let present age of Manoj is x years.
and their two sons present age are y and z years.
According to the question,
x = 2(y + z) ...(i)
Their ages after 20 years.
x + 20 = (y + 20) + (z + 20)
x = y + z + 20
From equation (1),
x = (x/2) + 20
x - (x/2) = 20
x/2 = 20
⇒ x = 40
Hence, present age of father = 40 years.

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