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# What is the sum of all digits of 2^13*5^7?

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 5600
GMAT 1: 800 Q59 V59
GPA: 3.82
What is the sum of all digits of 2^13*5^7? [#permalink]

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03 Aug 2017, 01:31
1
1
00:00

Difficulty:

15% (low)

Question Stats:

83% (01:14) correct 17% (01:25) wrong based on 69 sessions

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What is the sum of all digits of $$2^{13}5^7$$?

A. 3
B. 4
C. 6
D. 8
E. 10

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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
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"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Manager Joined: 30 Mar 2017 Posts: 69 Re: What is the sum of all digits of 2^13*5^7? [#permalink] ### Show Tags 03 Aug 2017, 01:34 2 5^7 and 2^7 will multiply to become 10^7 . After that we are left with 2^6 which will be 64 multiplied by 10^7. So sum of digits is 10 Sent from my Moto G (5) Plus using GMAT Club Forum mobile app Director Joined: 04 Dec 2015 Posts: 700 Location: India Concentration: Technology, Strategy Schools: ISB '19, IIMA , IIMB, XLRI WE: Information Technology (Consulting) Re: What is the sum of all digits of 2^13*5^7? [#permalink] ### Show Tags 03 Aug 2017, 04:55 3 1 MathRevolution wrote: What is the sum of all digits of $$2^{13}5^7$$? A. 3 B. 4 C. 6 D. 8 E. 10 $$2^{13}5^7$$ $$2^6*2^7*5^7$$ $$2^6(2^7*5^7)$$ $$2^6(10^7)$$ $$64(10^7)$$ $$64$$ and $$7$$ zeros $$= 640000000$$ Sum of all digits $$= 6 + 4 + 0 = 10$$ Answer (E)... _________________ Please Press "+1 Kudos" to appreciate. Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 5600 GMAT 1: 800 Q59 V59 GPA: 3.82 Re: What is the sum of all digits of 2^13*5^7? [#permalink] ### Show Tags 06 Aug 2017, 18:17 ==> You get $$2^{13}5^7=2^6(2^75^7)=64(10^7)=640,000,000.$$ The sum of the 0's at the back always becomes 0, so you get $$6+4=10.$$ The answer is E. Answer: E _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
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Target Test Prep Representative
Affiliations: Target Test Prep
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Re: What is the sum of all digits of 2^13*5^7? [#permalink]

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09 Aug 2017, 12:53
MathRevolution wrote:
What is the sum of all digits of $$2^{13}5^7$$?

A. 3
B. 4
C. 6
D. 8
E. 10

We can rewrite the given expression as:

2^6 x 2^7 x 5^7

2^6 x 10^7

64 x 10^7
Thus, 2^13 x 5^7 is the number 64 followed by 7 zeros and the sum of the digits is 6 + 4 = 10.

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Re: What is the sum of all digits of 2^13*5^7?   [#permalink] 09 Aug 2017, 12:53
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