Tips on Solving Aptitude Questions on Averages

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3 TIPS on cracking Aptitude Questions on Averages
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Tip 1 If terms are in progression, the average
is either the middle term or average of the two
middle terms
Question 1 Find the average of first 5 multiples
of 3. Solution Number of terms 5
odd. Average Middle term 3rd term 3x3
9 Question 2 The heights of 6 students in a
class are 5ft, 5.2ft, 5.4ft, 5.6ft, 5.8ft and 6ft
respectively. What is their average
height. Solution Average Average of middle
terms (5.45.6)/2 ft 5.5ft.
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Tip 2 If a person travels same distances with
different speeds, then the average speed is not
the arithmetic mean but the harmonic mean.
If a person covers a distance d first at x km/hr
and then covers the same distance d at y km/hr,
then the average speed is Total distance
travelled/ Total time taken 2d/ (d/x d/y)
2d/ (yd xd)/xy 2dxy/d(xy) 2xy/ xy
(Harmonic mean of x and y) Question A travels
25km at 50 km/hr and then 25km again with
70km/hr. What is As average speed during the
whole journey? Solution Average speed for the
whole journey (2x50x70) / (5070)
58.3km/hr
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Tip 3 When dealing with problems where average
changes by addition/ removal, create an equation
of the form New_total Old_Total
new_count old_count
/- Change in Average
Question The average weight of a class of 24
students is 35 kg. If the weight of the teacher
be included, the average rises by 400 g. What is
the weight of the teacher? Solution (24 35
Wteacher )/ 25 35 0.4 24 35 Wteacher 35
25 10 Wteacher 35 10 45 kgs
Question When a student weighing 45 kgs left a
class, the average weight of the remaining 59
students increased by 200g. What is the average
weight of the remaining 59 students? Solution Wr
emaining_students / 59 (Wremaining_students
45) / 60 0.2 60 Wremaining_students (59
Wremaining_students ) (59 45) (59
12) Wremaining_students / 59 45 12 57 kgs
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