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# The average (arithmetic mean) of the five numbers in a data set is 72.

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The average (arithmetic mean) of the five numbers in a data set is 72.  [#permalink]

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24 Aug 2018, 00:54
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89% (01:17) correct 11% (01:04) wrong based on 33 sessions

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[Math Revolution GMAT math practice question]

The average (arithmetic mean) of the five numbers in a data set is 72. The average (arithmetic mean) of the first three numbers is 98. What is the average (arithmetic mean) of the last two numbers?

A. 31
B. 32
C. 33
D. 34
E. 35

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"Only $79 for 1 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" NUS School Moderator Joined: 18 Jul 2018 Posts: 1021 Location: India Concentration: Finance, Marketing WE: Engineering (Energy and Utilities) Re: The average (arithmetic mean) of the five numbers in a data set is 72. [#permalink] ### Show Tags 24 Aug 2018, 00:59 Average of 5 number = 72. Sum of 5 = 72*5 = 360. Average of first 3 = 98. Sum of first 3 = 98*3 = 294. Difference of 360 and 294 = 66. The sum of the last two = 66. Average becomes 66/2 = 33. C is the answer. _________________ Press +1 Kudos If my post helps! GMAT Club Legend Joined: 12 Sep 2015 Posts: 4015 Location: Canada Re: The average (arithmetic mean) of the five numbers in a data set is 72. [#permalink] ### Show Tags 24 Aug 2018, 06:28 Top Contributor MathRevolution wrote: [Math Revolution GMAT math practice question] The average (arithmetic mean) of the five numbers in a data set is 72. The average (arithmetic mean) of the first three numbers is 98. What is the average (arithmetic mean) of the last two numbers? A. 31 B. 32 C. 33 D. 34 E. 35 Let a, b, c, d and e be the five numbers in the set. The average (arithmetic mean) of the five numbers in a data set is 72. So, (a + b + c + d + e)/5 = 72 Multiply both sides of the equation by 5 to get: a + b + c + d + e = 360 The average (arithmetic mean) of the first three numbers is 98. So, (a + b + c)/3 = 98 Multiply both sides of the equation by 3 to get: a + b + c = 294 What is the average (arithmetic mean) of the last two numbers? In other words, what is the average of d and e? Take a + b + c + d + e = 360 and replace a + b + c with 294 We get: 294 + d + e = 360 Subtract 294 from both sides to get: d + e = 66 So, the average of d and e = (d + e)/2 = 66/2 = 33 Answer: C RELATED VIDEO FROM OUR COURSE _________________ Test confidently with gmatprepnow.com Senior Manager Joined: 04 Aug 2010 Posts: 477 Schools: Dartmouth College Re: The average (arithmetic mean) of the five numbers in a data set is 72. [#permalink] ### Show Tags 24 Aug 2018, 06:58 MathRevolution wrote: [Math Revolution GMAT math practice question] The average (arithmetic mean) of the five numbers in a data set is 72. The average (arithmetic mean) of the first three numbers is 98. What is the average (arithmetic mean) of the last two numbers? A. 31 B. 32 C. 33 D. 34 E. 35 Sum = (quantity)(average). The average (arithmetic mean) of the five numbers in a data set is 72. Sum = 5*72 = integer with a UNITS DIGIT OF 0. The average (arithmetic mean) of the first three numbers is 98. Sum = 3*98 = integer with a UNITS DIGIT OF 4. For the sum of all 5 numbers to have a units digit of 0, the sum of the remaining 2 numbers must have a UNITS DIGIT OF 6, since INTEGER WITH A UNITS DIGIT OF 6 + INTEGER WITH A UNITS DIGIT OF 4 = INTEGER WITH A UNITS DIGIT OF 0. Only C will yield for the other 2 numbers a sum with a units digit of 6: 2*33 = 66. _________________ GMAT and GRE Tutor Over 1800 followers GMATGuruNY@gmail.com New York, NY If you find one of my posts helpful, please take a moment to click on the "Kudos" icon. Available for tutoring in NYC and long-distance. For more information, please email me at GMATGuruNY@gmail.com. Board of Directors Status: QA & VA Forum Moderator Joined: 11 Jun 2011 Posts: 4774 Location: India GPA: 3.5 WE: Business Development (Commercial Banking) Re: The average (arithmetic mean) of the five numbers in a data set is 72. [#permalink] ### Show Tags 24 Aug 2018, 07:34 MathRevolution wrote: [Math Revolution GMAT math practice question] The average (arithmetic mean) of the five numbers in a data set is 72. The average (arithmetic mean) of the first three numbers is 98. What is the average (arithmetic mean) of the last two numbers? A. 31 B. 32 C. 33 D. 34 E. 35 $$72*5 = 98*3 + 2*x$$ Or, $$360 = 294 + 2x$$ Or, $$x = 33$$, Answer must be (C) _________________ Thanks and Regards Abhishek.... PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS How to use Search Function in GMAT Club | Rules for Posting in QA forum | Writing Mathematical Formulas |Rules for Posting in VA forum | Request Expert's Reply ( VA Forum Only ) Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 8023 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: The average (arithmetic mean) of the five numbers in a data set is 72. [#permalink] ### Show Tags 26 Aug 2018, 18:24 => Let $$a, b, c, d$$ and $$e$$ be the five numbers. Now, the average of these numbers is $$\frac{( a + b + c + d + e )}{5}= 72$$, so $$a + b + c + d + e = 72 * 5 = 360$$. The average of the first three numbers is $$\frac{( a + b + c )}{3} = 98$$, so $$a + b + c = 98 * 3 = 294.$$ Thus, the sum of the last two numbers is $$d + e = ( a + b + c + d + e ) – ( a + b + c ) = 360 - 294 = 66.$$ Their average is $$\frac{( d + e )}{2} = \frac{66}{2} = 33.$$ Therefore, the answer is C. Answer: C _________________ 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 1 month Online Course"
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Re: The average (arithmetic mean) of the five numbers in a data set is 72.   [#permalink] 26 Aug 2018, 18:24
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