So Last Year

The sum of the digits of the number 100 0 2014 2014 1000^{2014}-2014 when expressed in decimal notation is?


The answer is 54372.

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2 solutions

Ivan Sekovanić
Jun 1, 2014

To begin with, let us notice that the number 100 0 2014 1000^{2014} is in fact a 1 1 followed by a lot of 0 0 's. In particular, it has 2014 3 = 6042 2014\cdot 3=6042 zeros in total.

Now let us also notice that any number in the form of 1 0 b 10^{b} , where b 5 b\geq 5 gives a somewhat similar result when you subtract 2014 2014 from it.

Let us look at a few examples:

100000 2014 = 97986 ; 100000-2014=97986 ; 1000000 2014 = 997986 ; 1000000-2014=997986 ; 10000000 2014 = 9997986 10000000-2014=9997986

Additionally, it always ends in the sequence 7986 7986 and has an N N number of 9 9 's in front of it, where N N is the number of digits of 1 0 b 10^{b} minus 5 5 (we lose 1 1 digit due to the subtraction and 4 4 are reserved for the ending sequence).

Now let us take a look at our problem again. 100 0 2014 1000^{2014} is indeed a number of the sort mentioned above, and thus we may apply the rules to it. Since it is a 6043 6043 digit number, we know that it will have 6038 6038 9 9 's and it will also end in 7986 7986 when you subtract 2014 2014 from it.

Finally, the sum of the digits of 100 0 2014 2014 1000^{2014}-2014 is 6038 9 + 7 + 9 + 8 + 6 = 54372 6038\cdot 9 +7+9+8+6=\boxed{54372}

dammit did a silly mistake calculated as 2014 zeroes in its expansion xD

Jitesh Mittal - 7 years ago

Same. Great solution! :D

Finn Hulse - 7 years ago

Did it in the same way!

Anik Mandal - 7 years ago

the topic got me once but still I was confident.......... this is the only solution I can think of, why it says Too easy, ain't it? This is very easy...... @Krishna Ar, you should add it to the set Are you smarter than a 5th grader?

Kartik Sharma - 7 years ago

Yo! did it in the same way!Thanks for writing.^_^

shuvayan ghosh dastidar - 6 years, 2 months ago
Bharath Kartha
Jun 1, 2014

1000^2014 has 2014 * 3 '0's . Now if we subtract 2014 from that number. We get 999999999 . . . 999997986. Number of 9s in this number =(3 * 2014)-4. Here 4 is subtracted as that the last four digits are different. Now adding 7+9+8+6+((3 2014)-4) 9) = 54372

Got answer as 54332 :(

Calculation mistake :/

Poonayu Sharma - 7 years ago

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ooh, that's a shame

Bharath Kartha - 6 years, 11 months ago

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