Aptitude - Average - Discussion

14. 

If the average marks of three batches of 55, 60 and 45 students respectively is 50, 55, 60, then the average marks of all the students is:

[A]. 53.33
[B]. 54.68
[C]. 55
[D]. None of these

Answer: Option B

Explanation:

Required average
= 55 x 50 + 60 x 55 + 45 x 60
55 + 60 + 45
= 2750 + 3300 + 2700
160
= 8750
160
= 54.68

Muneer.S said: (Sep 21, 2012)  
Total marks of first batch(55) is= 55*50=2750
Total marks of second batch (60)is= 60*55=3300
Total marks of third batch(45)= 45*60=2700

Total marks of second batch= 2750+3300+2700 = 8750
Total number of Students= 55+60+45 =160
Avg= 8750/160= 54.68

Madan said: (Jul 23, 2013)  
Average of Batch A = 55+60+45 = 160.
Average of Batch B = 50+55+60 = 165.

Average marks of all the students is = 160+165/6.

S.Balasubramaniam said: (Jan 3, 2014)  
Average of batch A & B = 55*50+60*55+45*60/55+60+45.

Total average number of batch = 8750/160.

Total average = 54.68.

Swordist said: (May 27, 2014)  
Total marks of first batch(55) is = 55*50 = 2750.
Total marks of second batch (60)is = 60*55 = 3300.
Total marks of third batch(45) = 45*60 = 2700.

Total marks of second batch = 2750+3300+2700 = 8750.
Total number of Students = 55+60+45 = 160.
Avg = 8750/160 = 54.6875 = 54.69.

Answer: D.

Vicky said: (Jun 17, 2016)  
Thanks, @Balasubramaniam.

Riyaz said: (Aug 15, 2016)  
Thank you all who has given suggestions while solving the problems.

Bhavik Oza said: (Nov 14, 2016)  
Average marks are asked. So how can 160 come in the denominator? If you keep 160 then you will get average students as your answer.

Sadhya said: (Aug 12, 2017)  
I tell trick here given students 55 60 45 . avg marks 50 55 60. let assume average as 50. first 55 students.

avg 50 given ok.but in case of next 60 members avg 55 given that means 60*5 = 300 extra .in case of remaining 45 students given 60 .that means 45*10 = 450 extra.totally 300 + 450 = 750 extra.

750 extra on 160 students so 750/160 = 4.68.finally 50 + 4.68 = 54.68 answer.

Keshav Singh said: (Sep 14, 2017)  
Thanks @S. Balasubramaniam.

Swa said: (Mar 15, 2018)  
Thank you @Sadhya.

Pranay Rk said: (Jul 30, 2018)  
It is clearly written 55, 60, 45 are total no of students. (i.e) 160 total student.

Whereas average marks of the student are 50, 55, 60.

Dr.R.Baskaran said: (Aug 3, 2018)  
55: 60:45 = 11:12:9.
Choose the origin (assumed average) as 55.
The sum of the deviations = 11x(-5) + 9x5 = -10.
Average = 55 - 10/(11 + 12 + 9) = 55 - 10/32.
You have to subtract about 1/3 which is nearly 0.33. The answer is 54.68.

Vijay Solanki said: (Aug 10, 2019)  
Let,
1st batch = A , 2nd batch = B , 3rd batch = C, Now,

A/55 = 50 => A= 2750 ( These are the Total marks of each batch of students ).
B/60 = 55 => B= 3300 ( These are the Total marks of each batch of students ).
C/45 = 60 => C= 2700 ( These are the Total marks of each batch of students ).

From above total marks of all batches => A+B+C = 2750+3300+2700 =>8750.

So, Total marks = 8750.
Total number of students in all 3 batches => 55+60+45 =160.

So, now we have to find average of all the students for that we will do,
Total marks / Total number of students = 8750 / 160 => 54.68.

Answer is option (B) = 54.68.

Hari said: (Jan 13, 2020)  
I am not understanding this, Anyone can explain it?

Bosski said: (Jan 18, 2020)  
Let assume average as 50. First 55 students.

Here Avg 50 is given. But in case of next 60 members avg 55 given that means 60*5 = 300 extra. In case of remaining 45 students given 60.45*10 = 450 extra.
And totally 300 + 450 = 750 extra.

750 extra on 160 students so 750/160 = 4.68.
And 50 + 4.68 = 54.68 answer.

Srid said: (Nov 15, 2020)  
Let T be total marks if all pupil, N be no of students, A be the average mark.
Case 1( when marks were entered correctly ie 63).
T/N=A.
Case 2(83)
(T+20)/N=A+0.5.
Subtract both equations.
20/N = 0.5.
N= 40.

Sourav said: (Jun 24, 2021)  
Given
students 55 60 45.
average marks 50 55 60.

You can take ratios of student in each batch.
i.e. 11 :12 : 9 (55/5:60/5:45/5).

Now solve;
=> 50x11+55x12+60x9 / (11+12+9),
=> 550+660+540/(32),
=> 1750/32,
=> 54.68.

Seema said: (Sep 28, 2021)  
Given;

Student 55 60 45
Average marks 50 55 60
According to formula;- avg=sum/no

Then;

avg = sum of marks(165)/ no of student(3).

Result comes 55.

Post your comments here:

Name *:

Email   : (optional)

» Your comments will be displayed only after manual approval.