GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 20 Sep 2018, 11:37

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Mary is building a pyramid out of stacked rows of soup cans. When comp

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 49271
Mary is building a pyramid out of stacked rows of soup cans. When comp  [#permalink]

### Show Tags

05 Jul 2018, 04:57
00:00

Difficulty:

55% (hard)

Question Stats:

60% (02:17) correct 40% (02:14) wrong based on 25 sessions

### HideShow timer Statistics

Mary is building a pyramid out of stacked rows of soup cans. When completed, the top row of the pyramid contains a single soup can, and each row below the top row contains 6 more cans than the one above it. If the completed pyramid contains 16 rows, then how many soup cans did Mary use to build it?

A. 91
B. 96
C. 728
D. 732
E. 736

_________________
BSchool Forum Moderator
Joined: 26 Feb 2016
Posts: 3131
Location: India
GPA: 3.12
Mary is building a pyramid out of stacked rows of soup cans. When comp  [#permalink]

### Show Tags

05 Jul 2018, 05:25
Bunuel wrote:
Mary is building a pyramid out of stacked rows of soup cans. When completed, the top row of the pyramid contains a single soup can, and each row below the top row contains 6 more cans than the one above it. If the completed pyramid contains 16 rows, then how many soup cans did Mary use to build it?

A. 91
B. 96
C. 728
D. 732
E. 736

We are told that the top row of the pyramid that Mary is building will contain 1 soup can.
The second row contains 7(1+6) cans. Similarly, the third row contains 12(1+2*6) cans.

This is an arithmetic progression and sum of the terms is $$\frac{n}{2}(2a + (n-1)d)$$

Substituting values - n = 16, a = 1 and d = 7, the sum of terms is $$8(2 + 15*7) = 8*107 = 736$$
Therefore, Mary needs 736(Option C) cans to build the pyramid of soup cans.

Shortcut solution:
Units digits of the 16 digits is {1 + 7 + 3 + 9 + 5}3 times + 1 = 3*15 + 1 = 75 + 1 = 76
Since, the units digit is 6 and number of soup can's > 96. The answer option is 736(Option E)

_________________

You've got what it takes, but it will take everything you've got

Manager
Joined: 31 Aug 2016
Posts: 103
Location: India
Concentration: Finance, General Management
GMAT 1: 680 Q49 V33
GPA: 2.81
Re: Mary is building a pyramid out of stacked rows of soup cans. When comp  [#permalink]

### Show Tags

05 Jul 2018, 08:27
Bunuel wrote:
Mary is building a pyramid out of stacked rows of soup cans. When completed, the top row of the pyramid contains a single soup can, and each row below the top row contains 6 more cans than the one above it. If the completed pyramid contains 16 rows, then how many soup cans did Mary use to build it?

A. 91
B. 96
C. 728
D. 732
E. 736

Row1 = 1
row 2 = 1 + 6
row 3 = 1 + 6*2
row 4 = 1 + 6*3
.
.
.
row 16 = 1 + 6 * 15

total cans = 16 + arithmetic sum of 6,12,18,....,90

= 16 + $$\frac{15}{2}$$(12 + 14 *6)

= 736

_________________

Resources
GMATNinja Webinars
GMATNinja Chats

Quant
Mixtures

Re: Mary is building a pyramid out of stacked rows of soup cans. When comp &nbs [#permalink] 05 Jul 2018, 08:27
Display posts from previous: Sort by

# Mary is building a pyramid out of stacked rows of soup cans. When comp

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

# Events & Promotions

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.