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UPSC 2016 CDS II Math Paper
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© examsnet.com
Question : 40
Total: 100
If the mean age of combined group of boys and girls is 18 years and the mean of age of boys is 20 and that of girls is 16, then what is the percentage of boys in the group ?
[2016 CDS-II]
60
50
45
40
Validate
Solution:
Let the number of boys and girls be x and y, respectively.
∴ Total age of boys and girls = Total age of boys + Total age of girls
⇒
(
x
+
y
)
×
18
=
x
×
20
+
y
×
16
⇒
18
y
−
16
y
=
20
x
−
18
x
⇒
2
y
=
2
x
⇒
y
=
x
∴ Percentage of boys in the group = 50%
© examsnet.com
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