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UPSC CDS 1 2020 Math Paper
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© examsnet.com
Question : 11
Total: 100
A two-digit number is 9 more than four times of the number obtained by interchanging its digits. If the product of digits in the two-digit number is 8, then what is the number?
81
42
24
18
Validate
Solution:
👈: Video Solution
x
y
=
8
⇒
y
=
8
x
(
10
x
+
y
)
=
4
(
10
y
+
x
)
+
9
10
x
+
y
=
40
y
+
4
x
+
9
6
x
=
39
y
+
9
2
x
=
13
y
+
3
2
x
=
104
x
+
3
2
x
2
−
3
x
−
104
=
0
⇒
x
=
8
,
13
2
∴
x
=
8
,
y
=
1
Required Number = 81
© examsnet.com
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