A welder needs to construct a closed cube-shaped tank with a volume of

10^5 for volume in a cube implies 10^2*10^2*10^2 which means that the surface area of a side is 10^2. Well, we want to build the total surface area so if cube has 6 sides then 6*100 = 600. Since the area covered by each sheet is 8 , then we have 600/8 = 75 sheets needed

E

Let me know if this is clear
Cheers
J

Dear jlgdr,
Forgive me, my friend, but I am going to correct a couple of mistakes in your approach, in an attempt to strengthen your understanding as well as the understanding of anyone else who chances upon this post.

First of all, 1 million = 1,000,000 = 10^6, not 10^5.

Second, the 1 million in this problem is 1 million liters, and the liter is a unit of volume. If you say that the cube is 10^2 = 100 on each edge, then that's 100 whats? a 100 cube-roots-of-a-liter?? You see, something becomes really funky about the units here. (In fact, a liter is a cubic decimeter, that is, a cube that is 10 cm on each side, but that would put the side of the cube at 100 decimeters, a most peculiar unit to employ.)

Finally, if the cube really were (10^2)*(10^2)*(10^2), then (10^2) would be the length of an edge, and (10^2)*(10^2) = 10^4 would be the area of a face. In general, if a cube has volume L^3, it has edge-length L, and each face has an area of L^2.

Your mistakes canceled, so you wound up with the correct answer. It's very important to appreciate when you get a question correct for correct reasons, and when you get it correct for incorrect reasons.

I hope all this helps.
Mike

Volume of tank = 10^6 liters -> 10^6/10^3 cubic m = 10^3

Volume of cube = a^3 -> a = 10 m
Surface area of cube = 6a^2 = 600 squared m
Area of one sheet = 4*2 = 8 squared m

N = 600/8 = 75 (E)

Solution:

Since 1,000 liters = 1 cubic meter, then 1,000,000 liters = 1,000 cubic meters. Therefore, a 1 million liter cube is a 1,000 cubic meter cube. Such a cube will have an edge length of 10 meters and a surface area of 6 x 10^2 = 600 square meters. Since each sheet of metal is 4 x 2 = 8 square meters, we need 600/8 = 75 such sheets to construct (the surface) of the cube-shaped tank.

Answer: E

Convert cubic liters to cubic meters:

1 million liters = 1000 cu.m.

Side of cube = cuberoot of (1000) = 10m.

Get the surface area of the cube = 6s^2 = 6(10)(10) = 600

Get number of metal sheets:

SA cube / A metal sheets

= 600 / 8 = 75.

E is the correct answer.

Can this question come for GMAT focus edition?

 

­
Yes, I believe so. This is a word problem involving some rudimentary geometry knowledge, which is considered by the GMAT as general knowledge rather than specific geometry.

­Alright sounds good, thanks Bunuel!