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UPSC 2015 CDS II Math Paper
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© examsnet.com
Question : 96
Total: 100
The average weight of students in a class is 43 kg. Four new students are admitted to the class whose weights are 42 kg, 36-5 kg, 39 kg and 42-5 kg respectively. Now the average weight of the students of the class is 42-5 kg. The number of students in the beginning was
[2015 CDS-II]
10
15
20
25
Validate
Solution:
Let the number of students in the beginning be n
Sum of weights of n students = 43n kg
When four new students areadmitted to the class:
Sum of weights of (n + 4) students
=
43
n
+
42
+
36.5
+
39
+
42.5
=
(
43
n
+
160
)
k
g
∴
43
n
+
160
n
+
4
=
42.5
⇒
43
n
+
160
⇒
42.5
n
+
170
⇒
0.5
n
=
10
⇒
n
=
20
© examsnet.com
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