In a certain brick wall, each row of bricks above the bottom

Expert replies

VJesus12: Legendary Member; Posts: 2276; Joined: Sat Oct 14, 2017 6:10 amFollowed by: 3 members

by VJesus12 » Sat Nov 23, 2019 2:33 am

In a certain brick wall, each row of bricks above the bottom row contains one less brick than the row just below it. If there are 5 rows in all and a total of 75 bricks in the wall, how many bricks does the bottom row contain?

(A) 14
(B) 15
(C) 16
(D) 17
(E) 18

[spoiler]OA=D[/spoiler]

Source: GMAT Paper Tests

Like this post

Source: Beat The GMAT — Problem Solving | Sat Nov 23, 2019 2:33 am

GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Sat Nov 23, 2019 7:54 am

VJesus12 wrote:In a certain brick wall, each row of bricks above the bottom row contains one less brick than the row just below it. If there are 5 rows in all and a total of 75 bricks in the wall, how many bricks does the bottom row contain?

(A) 14
(B) 15
(C) 16
(D) 17
(E) 18

Is working backwards a good way to solve this question?[/quote]
Let x = # of brick in bottom (1st) row
So x-1 = # of brick in 2nd row
So x-2 = # of brick in 3rd row
So x-3 = # of brick in 4th row
So x-4 = # of brick in 5th row

TOTAL # of bricks = 75

So, x + (x-1) + (x-2) + (x-3) + (x-4) = 75
Simplify: 5x - 10 = 75
5x =85
x = 17

Answer: D

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

Like this post

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

answer

by [email protected] » Sat Nov 23, 2019 9:56 am

Hi VJesus12,

We're told that in a certain brick wall, each row of bricks above the bottom row contains ONE FEWER brick than the row just below it, there are 5 rows in all and a TOTAL of 75 bricks in the walL. We're asked for the number of bricks in the bottom row. This question can be approached in a number of different ways - and if you recognize the pattern that this question is built around, you can solve it without too much work.

Since each of the 5 rows contains ONE FEWER brick than the row beneath it, we're dealing with 5 CONSECUTIVE integers. The AVERAGE of those 5 numbers will be the 'middle number'.... and with 75 total bricks and 5 rows, that 'middle number' will be 75/5 = 15. Thus, the other 4 rows will be 13 and 14.... and 16 and 17. We now know exactly how many bricks will be in each row, including the bottom row.

Final Answer: D

GMAT assassins aren't born, they're made,
Rich

Last edited by [email protected] on Tue Dec 03, 2019 10:02 am, edited 1 time in total.

Contact Rich at [email protected]

Like this post

GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8154; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Thu Nov 28, 2019 4:24 pm

VJesus12 wrote:In a certain brick wall, each row of bricks above the bottom row contains one less brick than the row just below it. If there are 5 rows in all and a total of 75 bricks in the wall, how many bricks does the bottom row contain?

(A) 14
(B) 15
(C) 16
(D) 17
(E) 18

[spoiler]OA=D[/spoiler]

Source: GMAT Paper Tests

We can let x = the number of bricks on the bottom row. We can create the equation:

x + (x - 1) + (x - 2) + (x - 3) + (x - 4) = 75

5x - 10 = 75

5x = 85

x = 17

Answer: D

Scott Woodbury-Stewart
Founder and CEO
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review