Aptitude - Average - Discussion
Discussion Forum : Average - General Questions (Q.No. 15)
15.
A pupil's marks were wrongly entered as 83 instead of 63. Due to that the average marks for the class got increased by half (1/2). The number of pupils in the class is:
Answer: Option
Explanation:
Let there be x pupils in the class.
| Total increase in marks = |  |
x x | 1 |  |
= | x |
| 2 | 2 |
 |
x | = (83 - 63)  |
x | = 20 x= 40. |
| 2 | 2 |
Discussion:
125 comments Page 1 of 13.
Mohd Saif said:
4 weeks ago
Sum1 = sum of (n-1) students + 83.
Sum2 = sum of (n-1) students + 63.
avg1 = Sum1/n;
avg2 = Sum2/n.
So, avg1-avg2 = 0.5.
Or, (83-63)/n = 0.5.
Then n=40.
Sum2 = sum of (n-1) students + 63.
avg1 = Sum1/n;
avg2 = Sum2/n.
So, avg1-avg2 = 0.5.
Or, (83-63)/n = 0.5.
Then n=40.
Sahr smk said:
3 months ago
Difference =20.
No of pupils = 20 divided increased number.
= 20/0.5,
= 40.
No of pupils = 20 divided increased number.
= 20/0.5,
= 40.
Usman Khan said:
10 months ago
Good session, thanks.
Sarika Jain said:
10 months ago
Thank you all.
Kavita said:
10 months ago
Thank you for explaining the answer.
(1)
Eliwa Mohamed Eliwa Salman said:
12 months ago
Assume number of pupils is x.
avg1 = 63/x --->eq (1)
avg2 = 83/x --->eq (2)
avg2 = avg1 + 0.5 ---> eq (3)
Substituting in eq (2) by eq (3).
(avg1) +0.5 = (83/x),
(63/x) +0.5 = (83/x),
(83/x) -(63/x) = 0.5,
(83-63)/x = 0.5,
20/x = 0.5,
x = 20/0.5 = 40.
avg1 = 63/x --->eq (1)
avg2 = 83/x --->eq (2)
avg2 = avg1 + 0.5 ---> eq (3)
Substituting in eq (2) by eq (3).
(avg1) +0.5 = (83/x),
(63/x) +0.5 = (83/x),
(83/x) -(63/x) = 0.5,
(83-63)/x = 0.5,
20/x = 0.5,
x = 20/0.5 = 40.
(11)
PaniniLuncher said:
1 year ago
My calculation:
1) The mistake is: 83-63 = 20.
2) Sum total after mistake = (sum + 20).
3) Avg after mistake = (avg + 0.5).
Therefore:
avg = sum/N.
(avg + 0.5) = (sum + 20)/N,
(sum/N) + 0.5 = (sum + 20)/N,
N(sum/N + 0.5) = (sum + 20),
sum + 0.5N = (sum + 20),
0.5N = 20 --> N = 40.
1) The mistake is: 83-63 = 20.
2) Sum total after mistake = (sum + 20).
3) Avg after mistake = (avg + 0.5).
Therefore:
avg = sum/N.
(avg + 0.5) = (sum + 20)/N,
(sum/N) + 0.5 = (sum + 20)/N,
N(sum/N + 0.5) = (sum + 20),
sum + 0.5N = (sum + 20),
0.5N = 20 --> N = 40.
(27)
Ajay Makala said:
3 years ago
Let pupils be x.
Given avg is increased by 1/2 after changing 83 to 63.
So, avg2 - avg1 = 1/2,
(sum2/x) - (sum1/x) =1/2,
(sum2 - sum1)/x = 1/2,
(83-63)/x=1/2,
20/x=1/2.
x = 40.
Given avg is increased by 1/2 after changing 83 to 63.
So, avg2 - avg1 = 1/2,
(sum2/x) - (sum1/x) =1/2,
(sum2 - sum1)/x = 1/2,
(83-63)/x=1/2,
20/x=1/2.
x = 40.
(121)
Random said:
3 years ago
Good Explanation, thanks all.
(10)
Tran said:
3 years ago
0.5 is a portion of (the sum of student's marks/no. of students). Therefore, if no of students is 40, then the sum of marks is 40, which is not true.
Please correct me, if I am wrong.
Please correct me, if I am wrong.
(6)
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