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# The formula for the sum of squares of integer between 1 and n is n(

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 5073
GMAT 1: 800 Q59 V59
GPA: 3.82
The formula for the sum of squares of integer between 1 and n is n( [#permalink]

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25 Sep 2017, 00:52
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Difficulty:

35% (medium)

Question Stats:

74% (01:29) correct 26% (01:29) wrong based on 43 sessions

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[GMAT math practice question]

The formula for the sum of squares of integer between 1 and n is n(n+1)(2n+1) / 6 = 1^2 + 2^2 + … + n^2. The is the value of 11^2 + 12^2 + … + 20^2?

A. 2470
B. 2475
C. 2480
D. 2485
E. 2490
[Reveal] Spoiler: OA

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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
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"Only $79 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" PS Forum Moderator Joined: 25 Feb 2013 Posts: 1008 Location: India GPA: 3.82 The formula for the sum of squares of integer between 1 and n is n( [#permalink] ### Show Tags 25 Sep 2017, 09:50 1 This post received KUDOS 2 This post was BOOKMARKED MathRevolution wrote: [GMAT math practice question] The formula for the sum of squares of integer between 1 and n is n(n+1)(2n+1) / 6 = 1^2 + 2^2 + … + n^2. The is the value of 11^2 + 12^2 + … + 20^2? A. 2470 B. 2475 C. 2480 D. 2485 E. 2490 Sum of squares from 1 to 20 $$= \frac{20*21*41}{6} = 2870$$ (use the formula given) Sum of squares from 1 to 10 $$= \frac{10*11*21}{6} = 385$$ Hence sum of squares from 11 to 20 $$=$$ Sum of squares from 1 to 20 $$-$$ sum of squares from 1 to 10 $$= 2870-385 = 2485$$ Option D Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 5073 GMAT 1: 800 Q59 V59 GPA: 3.82 Re: The formula for the sum of squares of integer between 1 and n is n( [#permalink] ### Show Tags 27 Sep 2017, 01:39 => 11^2 + 12^2 + … + 20^2 = ( 1^2 + 2^2 + … + 20^2 ) – (1^2 + 2^2 + … + 10^2) = 20∙21∙41/6 - 10∙11∙21/6 = 2870 – 385 = 2485 Ans: D _________________ 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$79 for 3 month Online Course"
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Re: The formula for the sum of squares of integer between 1 and n is n(   [#permalink] 27 Sep 2017, 01:39
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