Aptitude - Average
6.
The mean of five numbers is 18. If one number is excluded, their mean is 16. The excluded number is :
Answer
Total of 5 numbers = (18 x 5) = 90
Total of 4 numbers = (16 x 4) = 64
The excluded number = (90 − 64) = 26
Answer :
Option BExplanation :
Total of 5 numbers = (18 x 5) = 90
Total of 4 numbers = (16 x 4) = 64
The excluded number = (90 − 64) = 26
7.
Average of 2 numbers is 6.5 and square root of their product is 6. What are the numbers ?
Answer
Let the numbers be a and b. Then,
Average = a + b 2 = 6.5 ⇒ a + b = 13
√ab = 6 ⇒ ab = 36
(a − b)2 = (a + b)2 − 4ab = (13)2 − (4 x 36)
= (169 − 144) = 25 ⇒ (a − b) = 5
On solving a + b = 13 and a − b = 5, we get a = 9, b = 4.
Answer :
Option BExplanation :
Let the numbers be a and b. Then,
Average = a + b 2 = 6.5 ⇒ a + b = 13
√ab = 6 ⇒ ab = 36
(a − b)2 = (a + b)2 − 4ab = (13)2 − (4 x 36)
= (169 − 144) = 25 ⇒ (a − b) = 5
On solving a + b = 13 and a − b = 5, we get a = 9, b = 4.
8.
A man covers half of his journey at 6 kmph and the remaining half at 3 kmph. His average speed is
Answer
Average Speed = 2xy (x + y) kmph = 2 x 6 x 3 (6 + 3) kmph = 4 kmph
Answer :
Option CExplanation :
Average Speed = 2xy (x + y) kmph = 2 x 6 x 3 (6 + 3) kmph = 4 kmph
9.
The average age of 3 friends is 23. Even if the age of the 4th friend is added, the average remains 23. What is the age of the 4th friend ?
Answer
Sum of ages of 3 friends = (23 x 3) = 69 years
Sum of ages of 4 friends = (23 x 4) = 92 years
Age of the 4th friend = (92 − 69) = 23 years.
Answer :
Option BExplanation :
Sum of ages of 3 friends = (23 x 3) = 69 years
Sum of ages of 4 friends = (23 x 4) = 92 years
Age of the 4th friend = (92 − 69) = 23 years.
10.
The average marks in mathematics of 5 students was found to be 50. Later on, it was discovered that in case of 1 student, the marks 48 were misread as 84. The correct average is :
Answer
Total recorded marks = (50 x 5) = 250
Correct total = (250 + 48 − 84) = 214
Correct average = 214 5 = 42.8
Answer :
Option CExplanation :
Total recorded marks = (50 x 5) = 250
Correct total = (250 + 48 − 84) = 214
Correct average = 214 5 = 42.8
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