Averages – Section1

Question #1: What is the average of first 21 multiples of 7?
A) 49
B) 77
C) 66
D) 57

Option 'B' : 77
Hint:
Required average = 7(1+2+....+21) / 21
=(7/21)X ( (21x22) / 2 ) (because sum of first 21 natural numbers)
= 77

Question #2: In a class, the average age of 30 boys is 13 years and the average of 20 girls is 12 years. What is the average age of the whole class?
A) 12.4 Yrs
B) 12.5 Yrs
C) 12.6 Yrs
D) 12.7 Yrs

Option 'C' : 12.6 Yrs
Hint:
Total age of 50 students
(30X 13+20 X 12) = 630
Average = 630/50 = 12.6 Years

Question #3: The average of seven numbers is 18. The average of first three numbers is 14 and the average of last three numbers is 19. What is the middle number?
A) 30
B) 34
C) 23
D) 27

Option 'D' : 27
Hint:
The total of seven numbers = 7X18 = 126
The total of first 3 and last 3 numbers is = 3 X 14+3 X 19 = 99
So, the middle number is (126 - 99) = 27

Question #4: Average of 13 results is 65. If the average of first six results is 61 and average of last six results is 59. Find the seventh result.
A) 134
B) 125
C) 110
D) 157

Option 'B' : 125

Question #5: The average of 10 numbers is 25. The average of first three numbers is 22 1/3 and that of next five is 15 1/5. If the eighth be less than the ninth and tenth numbers by 5 and 11 respectively, then the tenth number is:
A) 67
B) 34
C) 45
D) 41

Option 'D' : 41

Question #6: The average of marks of a student of 8 exams was 35. How many marks must he get in the next exam so as to increase his average of marks by 5?
A) 80
B) 78
C) 54
D) 57

Option 'A' : 80

Question #7: Of the three numbers whose average is 45, the first is half of the sum of the others. The first number is:
A) 44
B) 87
C) 35
D) 45

Option 'D' : 45

Question #8: There were 45 students in a hostel, if the numbers of students increased by 7, the expenses of the mess were increased by Rs. 39 per day while the average expenditure per head diminished by Rs.1. What is the original expenditure of the mess?
A) Rs. 585
B) Rs. 577
C) Rs. 466
D) Rs. 857

Option 'A' : Rs. 585
Hint:
Let the original expenditure be Rs.X
Original average expenditure = X/45
New average expenditure = (X+39)/52
So (X/45) - ((X+39) / 52) = 1 so X = 585
So, original expenditure is Rs 585

Question #9: The average of seven numbers is 35. If one is included, the average become 40. The included number is:
A) 34
B) 82
C) 66
D) 75

Option 'D' : 75

Question #10: A man covered a certain distance at a speed of 8 kmph and returned at a speed of 4 kmph. Find the average speed of whole journey.
A) 5 1/3 kmph
B) 3 1/4 kmph
C) 4 1/3 kmph
D) 3 1/5 kmph

Option 'A' : 5 1/3 kmph

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