Math Is Fun Forum

Mathegocart

Member

Registered: 2012-04-29

Posts: 2,226

Silly problem

In the following sequence of numbers. each number has one mode 1 thean the preceding number. 1,11,111,1111,11111.... Which is the tens digit of the sum of the first 30 digits in the sequence?

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bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Silly problem

Hi;

Can you explain a bit more?

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thickhead

Member

Registered: 2016-04-16

Posts: 1,086

Re: Silly problem

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Bob

Administrator

Registered: 2010-06-20

Posts: 10,140

Re: Silly problem

hi Mathegocart

Which is the tens digit of the sum of the first 30 digits in the sequence?

eg.  In this number, 2468,  I would say it has four digits: 2 then 4 then 6 then 8.  So I'm guessing you mean the first 30 numbers in the sequence.

To get an answer:  All 30 have a units digit of 1.  29 of them also have a tens digit of 1.  What happens for the hundreds, thousands etc. doesn't affect the answer.  So compute 30 x 1 + 29 x 10 and look at the tens digit of your answer.

Bob

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