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 3 of 13.
Selva ganesh said:
5 years ago
Let us consider p be the no. of pupil, x be the average.
Case1: Original marks 63/p=x -----> average of case 1.
Case2: New marks 83/p=x+1/2 ----> average of case 2.
2-1 => (83/p-63/p) = x+1/2-x.
=> 20/p = 1/2,
=> p = 40.
Case1: Original marks 63/p=x -----> average of case 1.
Case2: New marks 83/p=x+1/2 ----> average of case 2.
2-1 => (83/p-63/p) = x+1/2-x.
=> 20/p = 1/2,
=> p = 40.
(1)
Kavita said:
1 year ago
Thank you for explaining the answer.
(1)
Android said:
2 decades ago
I didn't understand the logic. Please explain.
Praveen said:
2 decades ago
Please explain.
Arun said:
2 decades ago
Can you explain it briefly please ?
Arunoid said:
2 decades ago
Please help the needy and me too.
Krishna kanth said:
2 decades ago
I didn't understand anything please please please some body explain.
Rakesh said:
2 decades ago
If mark=63,then total mark(mark1+mark2+---+63) =(average mark*x)-(1)
but in the qst given that enterd mark is 83 instead of 63,then avg is increased by 1/2(half),
then total mark(mark1+mark2+----+83)=(avg mark+1/2)*x -(2)
eq(2)-eq(1)
83-63=1/2*x;
x=20*2=40
but in the qst given that enterd mark is 83 instead of 63,then avg is increased by 1/2(half),
then total mark(mark1+mark2+----+83)=(avg mark+1/2)*x -(2)
eq(2)-eq(1)
83-63=1/2*x;
x=20*2=40
Swathy said:
2 decades ago
Rakesh I cant understand your logic can you explain clearly?.
Nik said:
2 decades ago
Avg = sum of marks of each studnt/total no of studnts
= s/n
according to the given condition
(s+20)/n = (s/n)+0.5 ....(here 1/2 is considered as 0.5)
cross multiplying we get,
s+20 = s + 0.5n
so, n = 40
= s/n
according to the given condition
(s+20)/n = (s/n)+0.5 ....(here 1/2 is considered as 0.5)
cross multiplying we get,
s+20 = s + 0.5n
so, n = 40
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