A certain lighthouse is a tall thin cylinder of brick, with a light ch

Question

A certain lighthouse is a tall thin cylinder of brick, with a light chamber at the top. The brick extends from the ground to the floor of the light chamber. The brick siding of lighthouse is in need of painting. How many square feet of brick does it have?

(1) The outer diameter of the brick portion of the lighthouse is 28 ft
(2) There are 274 steps from ground level to the floor of the light chamber, and each one is 8 inches high.
 
 Kudos for a correct  solution .

ynaikavde · Answer

1) gives us the radius but no information on height insufficient
2) gives us height info but no radius insufficient

together we can get surface area hence answer is C.

karan14 · Answer

C for Sure.
We are asked to find Total surface area of light house.

Option A will give us radius/diameter with which we can calculate the area of the floor of light chamber but to calculate lateral surface area we need height of the tower,which we will get from option B. 
Using A and B together we will get Radius/diameter and Height ..so we can calculate the total Surface area of the cylinder.

Hence Answer should be C.

DesiGmat · Answer

Here we go,

Total Surface Area of Cylinder = 2πr(h+r)

St1 and St2 provides the required info.

Option C is correct

Bunuel · Answer

MAGOOSH OFFICIAL SOLUTION:

The lighthouse is essentially a cylinder, and the area that needs to be painted is the lateral surface area. We would need both r and h to calculate this.

Statement #1 tells us diameter = 28, which means radius = 14. We know the radius, but not the height. Statement #1 by itself is insufficient.

In Statement #2, the 274 steps go from the very bottom to the very top of the cylinder in question. We know each step is 8 inches, so the total height traversed by the steps is 274*8 in. We would have to change that result from inches to feet, but essentially, with this piece of information, we have the height. We know the height, but not the radius. Statement #2 by itself is insufficient.

Combined. Statement #1 gives us the radius, statement #2 gives us the height, and we’re in business! We now have enough information to calculate the lateral surface area. Combined, the statements are sufficient.

Answer = C.

Bunuel · Answer

Check other  3-D Geometry Questions  in our  Special Questions Directory .

Archit3110 · Answer

#1
we have radius but no info of height ; insufficient
#2
we have height but no info of radius
insufficient
from 1 &2
we can find both vol and TSA
sufficient
IMO C

Businessconquerer · Answer

I UNDERSTAND WHY PEOPLE CHOSE TO MARK C AS THE ANSWER, BUT

THE BRICK SIDING IS ON BOTH SIDES OF LIGHTHOUSE, WHAT THEY ARE ASKING US IS WHATS THE TOTAL SURFACE AREA OF THE BRICK SIDING.
WHY HAVE WE NOT CONSIDERED THE INNER DIAMETER?

BECAUSE IT DOESN'T SPECIFY HOW THE STAIRS SYNC TO THE WALLS. THEY CAN BE SEPARATE

dcummins · Answer

Just an observation. A brick portion = area between outer circle and inner circle of the concentric circle formed, right?

That needs to be true for us to use A.

bumpbot · Answer

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.

A certain lighthouse is a tall thin cylinder of brick, with a light ch

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Data Sufficiency (DS) Questions

A certain lighthouse is a tall thin cylinder of brick, with a light ch

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards