The ones who are crazy enough to think they can change the world are the ones who do.

- Steve Jobs

Tricky Interview Questions on Average

Average - Aptitude

11. Jiju obtained 80, 75, 77, 92 and 86 marks (out of 100) in English, Mathematics, Physics, Chemistry and Biology What are his average marks?

x

Option: C

Explanation

average =

80 + 75 + 77 + 92 + 86

average = 82

✉ Answer

12. In Mari Selvan's Opinion, his weight is greater than 65 kg but less than 72 kg. His brother does not agree with Mari Selvan and he thinks that Mari Selvan's weight is greater than 60 kg but less than 70 kg. His mother's view is that his weight cannot be greater than 68 kg. If all of them are correct in their estimation, What is the average of different probable weights of Mari Selvan?

x

Option: A

Explanation

Let Mari Selvan's weight be X kg

Acoording to Mari Selvan, his weight seems to be between 65 kg and 72 kg. i.e) 65 < X < 72

Acoording to Mari Selvan's brother, his weight seems to be 60 kg and 70 kg. i.e) 60 < X < 70

Acoording to Mari Selvan's mother, his weight seems to be less than 68 kg. i.e) X < 68

from the above condition, the value's that is satisfying the conditions are 66 kg and 67 kg

Average =

66 + 67

133

= 66.5 kg

✉ Answer

13. The average of 20 numbers is zero. Of them at most, how many may be greater than zero?

x

Option: C

Explanation

there can 19 numbers greater than zero

assume sum of 19 numbers be a

20th number be - a

average =

a - a

= 0

✉ Answer

14. If the mean of a, b, c is M and ab + bc + ca = 0, then the mean of a², b², c² is:

x

Option: D

Explanation

we know that

a + b + c

= M

a + b + c = 3M

squaring on both sides, (a + b + c)² = (3M)²

a²+ b² + c² + 2(ab + bc + ca) = 9M²

we know that ab + bc + ca = 0, .i.e) a² + b² + c² = 9M²

now, average =

a²+ b²+ c²

9M²

=3M²

✉ Answer

15. Distance between two stations A and B is 778 km. A train covers the journey from A to B at 84 km per hour and returns back to A with a uniform speed of 56 km per hour. Find the average speed of the train during the whole journey.