Question

The average of twelve positive numbers is 15. If the average of the first four
numbers is 9 and that of the last four numbers is 26. what is the average of the
remaining four numbers ?
1) 15
2) 20
3) 25
4 10
5) 12
​

Answer 1

Answer:

Option 4). 10

Step-by-step explanation:

We know that:

Average = Sum of observations / No. of observations

=> Sum of observations = Average * No. of observations

Average of 12 numbers = 15

=> Sum of 12 numbers = 15 * 12 = 180 ....(i)

Average of first 4 numbers = 9

=> Sum of first 4 numbers = 9 * 4 = 36 .....(ii)

Average of last 4 numbers = 26

=> Sum of last 4 numbers = 26 * 4 = 104 ...(iii)

Let the sum of remaining 4 numbers = S

Clearly,

Sum of remaining four numbers = Sum of all 12 numbers - Sum of first four numbers - Sum of last four numbers

Therefore:

S = 180 - 36 - 104

S = 40

Average of remaining 4 numbers = S/4

                                                        = 40/4

                                                         = 10

Average of remaining 4 numbers = 10 (Option 4.)