The sum of the digits of the number 10n-1 is 3798

The sum of the digits of the number 10n-1 is 3798

Postby Guest » Tue Feb 12, 2013 4:10 am

The sum of the digits of the number 10n-1 is 3798 .The value of n is?





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Re: The sum of the digits of the number 10n-1 is 3798

Postby Jonasmathwork » Tue Aug 13, 2013 6:17 am

Solution: Given sum of 10n-1=3798
by this we can find first term 10n-1 put n=1 we get 9
second term put n=2 we get 19
a=9
d=second term-first term
d=10
Sn=3798
by AP we have Sn=[2a+(n-1)d]
3798=[2*9+(n-1)10]
3798=[18+10n-10]
3798=[8+10n]
n=379
there for the nth term is 379.

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