Sequence And Series Question 150
Question: $ 11^{3}+12^{3}+….+20^{3} $
[Pb. CET 1997; RPET 2002]
Options:
A) Is divisible by 5
B) Is an odd integer divisible by 5
C) Is an even integer which is not divisible by 5
D) Is an odd integer which is not divisible by 5
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Answer:
Correct Answer: B
Solution:
$ \sum\limits_{n=1}^{20}{(n^{3})}-\sum\limits_{n=1}^{10}{(n^{3})}=[ \frac{n(n+1)}{2} ]{n=20}^{2}-[ \frac{n(n+1)}{2} ]{n=10}^{2} $
Þ $ s_2={{[ \log ,5/3 ]}^{2}} $ = 44100 - 3025 = 41075.
BETA
