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 9 of 13.
Arushi Mathur said:
7 years ago
Let x = total no of students, y=Avg of students when 63 is taken.
Sum of students when 63 is taken=xy.
So, (xy-63+83) /x=y+0.5.
(xy-20) =xy-0.5x.
x = 40.
Sum of students when 63 is taken=xy.
So, (xy-63+83) /x=y+0.5.
(xy-20) =xy-0.5x.
x = 40.
Sheik said:
7 years ago
Thanks @Ravi.
Ashwini said:
7 years ago
See the difference 83 and 63, which means extra 20 marks they have given. It increased by 1/2 means we shoud divide 20 by 1/2 which is nothing but 40.
Royal said:
7 years ago
Nice explanation @Nik.
Mudit said:
7 years ago
I didn't understand why we are multiplying x with 1/2? Please tell me.
Deepak said:
7 years ago
Let avg.+1/2 = y+83/x- ------> eq1.
Y=remaining student's marks.
X =total no of students.
Now avg.= y+63/x-----> eq2
Eq2-eq1.
83-63/x=1/2.
X=40.
Y=remaining student's marks.
X =total no of students.
Now avg.= y+63/x-----> eq2
Eq2-eq1.
83-63/x=1/2.
X=40.
Pawan yadav said:
7 years ago
Let x = total number of student.
Increase 1/2 means x * 1/2 = x/2,
Means x/2 = 83-63
x = 40.
Increase 1/2 means x * 1/2 = x/2,
Means x/2 = 83-63
x = 40.
Arun said:
7 years ago
83-63/.5 = 40.
Natasha said:
7 years ago
Let 'x' be the avg marks and 'y' be the no of pupils due to entering 83 instead of 63 the avg mark 'x' became 'x + 0.5'. Please note that the avg was increased by 0.5 = 1/2 and not by x/2. Since the difference between 83 answer 63 yields 20 which is divided among y pupils.
y/2 =20 gives y=40.
y/2 =20 gives y=40.
Vinodha said:
7 years ago
I didn't understand this please explain clearly.
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