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UPSC NDA I 2010 Mathematics Paper
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© examsnet.com
Question : 109
Total: 120
What is the sum of all natural numbers between 200 and 400 which are divisible by 7 ?
6729
8712
8729
9276
Validate
Solution:
a
=
203
;
L
=
399
L
=
a
+
(
n
−
1
)
d
∴
399
=
203
+
(
n
−
1
)
×
7
or
399
−
203
=
(
n
−
1
)
7
or
28
=
n
−
1
⇒
n
=
29
Sum
=
29
2
[
a
+
L
]
=
29
2
[
203
+
399
]
=
8729
© examsnet.com
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