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UPSC 2016 CDS I Math Paper
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© examsnet.com
Question : 12
Total: 100
If
4
x
2
y
=
128
and
3
3
x
3
2
y
−
9
x
y
=
0
,
then the value of
x
+
y
can be equal to
[2016 CDS-I]
7
5
3
1
Validate
Solution:
4
x
2
y
=
128
⇒
2
2
x
+
y
=
2
7
⇒
2
x
+
y
=
7
......(1)
3
3
x
3
2
y
−
9
x
y
=
0
⇒
3
3
x
+
2
y
=
3
2
x
y
⇒
3
x
+
2
y
=
2
x
y
.....(2)
From (1), we have
4
x
+
2
y
=
14
...(3)
Subtracting (2) from (3), we have
x
=
14
−
2
x
y
⇒
x
(
2
y
+
1
)
=
2
×
7
⇒
x
(
2
y
+
1
)
=
2
×
(
2
×
3
+
1
)
∴
x
=
2
and
y
=
3
⇒
x
+
y
=
5
© examsnet.com
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