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Question

If 11+103+1005+n terms=10n+1+xn2+y9, then the value of xy is

A
19
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B
19
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C
1
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D
1
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Solution

The correct option is A 19
Let Sn=11+103+1005+to n terms
Now,
Sn=(10+1)+(100+3)+(1000+5)+{10n+(2n1)}Sn=(10+102+103++10n)+(1+3+5++(2n1))Sn=[10×(10n1)101+n2(1+2n1)]Sn=109(10n1)+n2Sn=10n+1+9n2109x=9,y=10xy=19

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