GMAT Official Guide 2019 Over the past 7 weeks

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BTGmoderatorDC: Moderator; Posts: 7187; Joined: Thu Sep 07, 2017 4:43 pmFollowed by: 23 members

by BTGmoderatorDC » Tue Jul 03, 2018 4:44 pm

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Over the past 7 weeks, the Smith family had weekly grocery bills of $74, $69, $64, $79, $64, $84, and $77. What was the Smiths' average (arithmetic mean) weekly grocery bill over the 7-week period?

A. $64

B. $70

C. $73

D. $74

E. $85

Source: Beat The GMAT — Problem Solving | Tue Jul 03, 2018 4:44 pm

Shahrukh_mbabreakspace: Senior | Next Rank: 100 Posts; Posts: 32; Joined: Mon Jul 02, 2018 1:56 amFollowed by: 2 members

by Shahrukh_mbabreakspace » Wed Jul 04, 2018 2:21 am

Average= Sum of all bills/7
Sum of all bills = 511
Average = 511/7= 73

Alternatively,
If we assume average to 70 and just look at the distortions and then just edit the answer:
So it becomes(+4-1-6+9-6+14+7)= 21
21/7=3

70+3=73

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16206; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Wed Jul 04, 2018 6:25 am

BTGmoderatorDC wrote:Over the past 7 weeks, the Smith family had weekly grocery bills of $74, $69, $64, $79, $64, $84, and $77. What was the Smiths' average (arithmetic mean) weekly grocery bill over the 7-week period?

A. $64

B. $70

C. $73

D. $74

E. $85

Average = ($74 + $69 + $64 + $79 + $64 + $84 + $77)/7
= $511/7
= $73

Answer: C

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Brent

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8246; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Sun Jul 22, 2018 5:43 pm

BTGmoderatorDC wrote:Over the past 7 weeks, the Smith family had weekly grocery bills of $74, $69, $64, $79, $64, $84, and $77. What was the Smiths' average (arithmetic mean) weekly grocery bill over the 7-week period?

A. $64

B. $70

C. $73

D. $74

E. $85

We can determine the average using the formula: average = sum/quantity:

average = (74 + 69 + 64 + 79 + 64 + 84 + 77)/7 = 511/7 = 73

Answer: C

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regor60: Master | Next Rank: 500 Posts; Posts: 416; Joined: Thu Oct 15, 2009 11:52 am; Thanked: 27 times

by regor60 » Mon Jul 23, 2018 5:23 am

BTGmoderatorDC wrote:Over the past 7 weeks, the Smith family had weekly grocery bills of $74, $69, $64, $79, $64, $84, and $77. What was the Smiths' average (arithmetic mean) weekly grocery bill over the 7-week period?

A. $64

B. $70

C. $73

D. $74

E. $85

Just add up the one's digits and keep track the running sum's one's digit.

Final one's digit is a 1. Since the overall sum is divisible by 7, the average must end in 3. The only answer that meets this is C, 73

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