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Averages ( 6 to 10 ):
APTITUDE QUESTIONS (AVERAGES):
6. If the average marks of three batches of 55, 60 and 45 students respectively are 50, 55 and 60, then the average marks of all the students is:
A) 53.33
B) 54.68
C) 55
D) 60
E) None of these
View Answer
Answer: option (B)
Explanation:
Required Average = [ (55*50+60*55+45*60)/(55+60+45) ]= (2750+3300+2700)/160 = 8750/160 = 54.68
7. Of the four numbers, whose average is 60, the first is one-fourth of the sum of the last three. The first number is:
A) 15
B) 45
C) 48
D) 60.25
E) None of these
View Answer
Answer: option (C)
Explanation:
Le the first number be x.
Then, the sum of the four numbers = x + 4x = 5x.
So, 5x/4 =60 or x = (60*4)/5=48
8. If the arithmetic mean of seventy-five numbers is calculated, it is 35. If every number is increased by 10, then the mean of new numbers is:
A) 45
B) 30
C) 70
D) 90
E) None of these
View Answer
Answer: option (A)
Explanation:
Arithmetic Mean of 75 numbers = 35
The sum of 75 numbers = (75 * 35) = 2625
Total increase = (75 * 10) = 750
Increased sum = (2625 + 750) = 3375
Increased average = 3375/75}=45
9. The average of ten numbers is 7. If each number is multiplied by 12, then the average of the new set of numbers is:
A) 7
B) 19
C) 82
D) 84
E) None of these
View Answer
Answer: option (D)
Explanation:
Average of 10 numbers = 7
The sum of these 10 numbers is = (10 * 7) = 70
∴ x1 + x2 + ……+ x10 = 70
=> 12×1 + 12×2 + ……+ 12×10 = 840
=> (12×1 + 12×2 + … + 12×10)/10}=84
=> Average of new numbers is 84.
10. The average number of 11 numbers is 10.9. The average of the first 8 numbers is 10.5 and that of the last 8 numbers is 11.4, then what is the middle number:
A) 51
B) 41.3
C) 51.4
D) 55.3
E) None of these
View Answer
Answer: option (D)
Explanation:
Middle number = [(10.5 * 8 + 11.4 * 8) – 10.9 * 11] = (175.2 – 119.9) = 55.3