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UPSC CDS Math Average Questions
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© examsnet.com
Question : 7
Total: 23
Consider two-digit numbers which remain the same when the digits interchange their positions. What is the average of such two-digit numbers ?
[2019 CDS-I]
33
44
55
66
Validate
Solution:
Such numbers are 11, 22, 33, .….99
Sum of numbers
=
11
+
22
+
33
+
.
…
.
+
99
=
11
(
1
+
2
+
3
+
…
.
.
+
9
)
=
11
×
9
×
10
2
=
495
Required average
=
495
9
=
55
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