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# What is the sum of digits of number 10^28 – 28?

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Current Student
Joined: 11 May 2008
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What is the sum of digits of number 10^28 – 28?  [#permalink]

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22 Jul 2008, 19:09
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77% (01:37) correct 23% (01:55) wrong based on 179 sessions

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What is the sum of digits of number 10^28 - 28?

(A) 227
(B) 228
(C) 236
(D) 237
(E) 243
Current Student
Joined: 11 May 2008
Posts: 499
Re: What is the sum of digits of number 10^28 – 28?  [#permalink]

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23 Jul 2008, 05:08
2
4
100=10^2
1000=10^3.
so 100-28=72 . so sum= 9
1000-28=972. sum= 9+9
so 10^28= 9+9+9......27times( i.e 28 -1 times)= 27*9=243
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Re: What is the sum of digits of number 10^28 – 28?  [#permalink]

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22 Jul 2008, 20:30
arjtryarjtry wrote:
What is the sum of digits of number 10^28-28?
(A) 227
(B) 228
(C) 236
(D) 237
(E) 243

It will be 9*26+7+2 = 243

E
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Re: What is the sum of digits of number 10^28 – 28?  [#permalink]

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23 Jul 2008, 05:03
i dont quite follow ... isnt 10^28 just 1 followed by 28 zeroes ... i.e. the sum of the digits of that number would be just 1, no ?
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Re: What is the sum of digits of number 10^28 – 28?  [#permalink]

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23 Jul 2008, 05:04
pmenon wrote:
i dont quite follow ... isnt 10^28 just 1 followed by 28 zeroes ... i.e. the sum of the digits of that number would be just 1, no ?

Its 10^28 - 28 So number will be 26 9s followed by 72 whose sum is 243
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Joined: 09 Feb 2011
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Re: What is the sum of digits of number 10^28 – 28?  [#permalink]

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09 Feb 2011, 13:09
1
What is the sum of digits of number 10^28 – 28?

(A) 227
(B) 228
(C) 236
(D) 237
(E) 243
Manager
Joined: 27 Oct 2010
Posts: 90
Re: What is the sum of digits of number 10^28 – 28?  [#permalink]

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09 Feb 2011, 14:13
1
1000-28=972
for 3 zeroes = 9+7+2
for 28 zeroes = 26*9+7+2=27*9=..3
E
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Re: What is the sum of digits of number 10^28 – 28?  [#permalink]

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20 Apr 2014, 21:29
$$10^{28}-28$$

This expression will give all 9's with 72 at the end

99999999......72

Addition of all 9's with 72 will always give a number which is divisible by 9

Only option E = 243 stands out

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Posts: 59590
Re: What is the sum of digits of number 10^28 – 28?  [#permalink]

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20 Apr 2014, 23:57
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Re: What is the sum of digits of number 10^28 – 28?  [#permalink]

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23 Feb 2015, 23:08
1
Dear Moderators,

I agree with the correct answer that is given in the thread, but could one of you place it in the original post - I'm sure that other users would like to have it there.

GMAT assassins aren't born, they're made,
Rich
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Re: What is the sum of digits of number 10^28 – 28?  [#permalink]

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24 Feb 2015, 04:41
EMPOWERgmatRichC wrote:
Dear Moderators,

I agree with the correct answer that is given in the thread, but could one of you place it in the original post - I'm sure that other users would like to have it there.

GMAT assassins aren't born, they're made,
Rich

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Done. Thank you.
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What is the sum of digits of number 10^28 – 28?  [#permalink]

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03 Oct 2018, 02:26
arjtryarjtry wrote:
What is the sum of digits of number 10^28 - 28?

(A) 227
(B) 228
(C) 236
(D) 237
(E) 243

Such question may very well be dealth with Induction method

$$10^2-28 = 100-28 = 72$$ i.e. no digit as 9 and last two digits are 7 and 2

$$10^3-28 = 1000-28 = 972$$ i.e. One digit as 9 and last two digits are 7 and 2

$$10^4-28 = 10000-28 = 9972$$ i.e. Two digits as 9 and last two digits are 7 and 2

---
---

$$10^{28}-28 =$$ Twenty six digits as 9 and last two digits are 7 and 2

i.e.e Sum of digits $$= 26*9 +7+2 = 243$$

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What is the sum of digits of number 10^28 – 28?   [#permalink] 03 Oct 2018, 02:26
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