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:
123 comments Page 1 of 13.
Android said:
1 decade ago
I didn't understand the logic. Please explain.
Praveen said:
1 decade ago
Please explain.
Arun said:
1 decade ago
Can you explain it briefly please ?
Arunoid said:
1 decade ago
Please help the needy and me too.
Krishna kanth said:
1 decade ago
I didn't understand anything please please please some body explain.
Rakesh said:
1 decade 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:
1 decade ago
Rakesh I cant understand your logic can you explain clearly?.
Nik said:
1 decade 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
Sachin Bende said:
1 decade ago
@ swathy
rakesh's logic is absolutely correct..
explanation:
=(avg mark+1/2)*x - (avg mark*x)
taking "x" common we get,
=x(avg mark + 1/2 - avg mark)
cancelling avg mark
hence,we get
= x(1/2)= 1/2*x
therefore,
83-63=1/2*x
x=20*2=40
ok got it.
rakesh's logic is absolutely correct..
explanation:
=(avg mark+1/2)*x - (avg mark*x)
taking "x" common we get,
=x(avg mark + 1/2 - avg mark)
cancelling avg mark
hence,we get
= x(1/2)= 1/2*x
therefore,
83-63=1/2*x
x=20*2=40
ok got it.
Habib said:
1 decade ago
Frnz....dnt get confused boy that 1/2 factor !!!!
see,
(total marks)/(no. of pupils)= avg
OR
total marks = avg X no. of pupils
Given, increase is of 1/2 , no. of pupils=x
total marks increased : 83-63 = 20
Hence, for 1/2 mark avg increase, we use
20 = (1/2) * x OR x=40
see,
(total marks)/(no. of pupils)= avg
OR
total marks = avg X no. of pupils
Given, increase is of 1/2 , no. of pupils=x
total marks increased : 83-63 = 20
Hence, for 1/2 mark avg increase, we use
20 = (1/2) * x OR x=40
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