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UPSC CDS 1 2020 Math Paper
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© examsnet.com
Question : 41
Total: 100
The number of three digit numbers (all digits are different) which are divisible by 7 and also divisible by 7 on reversing the order of the digits, is
Six
Five
Four
Three
Validate
Solution:
👈: Video Solution
100
x
+
10
y
+
z
is divisible by 7.
100
z
+
10
y
+
x
is divisible by 7.
⇒
(
99
x
−
99
z
)
is divisible by 7
⇒
x
−
z
is divisible by 7
∴ 8y1 or 9y2
⇒ 861,952 & 168,258
⇒ four possible values.
© examsnet.com
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