Ladybird Posted October 8, 2012 Share Posted October 8, 2012 (edited) Hello Evrybody! Sorry if I post this in the wrong area! I am studying like crazy for the GRE, and I didnt do math since... fiou.. 3 years?? I have 2 questions for you. I can't understand the explanations given by the practice test, i bold the things that doesn't make sense to me : 1- What is he surface area of a cube with volume = 512 united cubed ? Answer: the volume of a cube is s^3 (s x s x s), so s^3 = 512 and so s=8. Surface area of 1 side = 8x8 = 64, so for the 6 sides = 384 2- I couldn't understant how they find z : 9 million = (z / 100) x 0,75 million z = 1200 % Thank you so much for your help! And good luck for the people taking the GRE Edited October 8, 2012 by Ladybird Link to comment Share on other sites More sharing options...

aberrant Posted October 9, 2012 Share Posted October 9, 2012 1- What is he surface area of a cube with volume = 512 united cubed ? Answer: the volume of a cube is s^3 (s x s x s), so s^3 = 512 and so s=8. Surface area of 1 side = 8x8 = 64, so for the 6 sides = 384 S = the length of 1 side. Because the volume of a cube = width x length x height, and they are all the same, therefore s x s x s = s^3 = 512. Take the cube root of 512, you get 8. 2- I couldn't understant how they find z : 9 million = (z / 100) x 0,75 million z = 1200 % I believe you're missing the percentage sign in (z / 100). It should be (z / 100%). Rewrite the following on a piece of paper. 1) In the American way: 9 million = (z / 100%) x 0,75 million (9 million / 0.75 million) = (z / 100%) x (0.75 million / 0.75 million) 12 = (z / 100%) x 1 12 = (z / 100%) 12 x 100% = (z / 100%) x 100% 1200% = z Hence. z = 1200% 2) Using the Asian way: 9 million = (z / 100%) x 0,75 million 9/0.75 = z / 100% 12 * 100% = z z = 1200% Good luck in your GRE. Link to comment Share on other sites More sharing options...

Instigate Posted October 9, 2012 Share Posted October 9, 2012 For the first one try guessing. You know that s x s x s = 512. Now, try 3 x 3 x 3 = 27, so you need a bigger number. Try 10 x 10 x 10 = 1000 so smaller, and so on. When you do a lot of those problems you start to get a feeling where the number should be. Like if it were 1567 then you know that it is more than 10, but not too much more. 9m=(z/100) x 0.75m 9/0.75=z/100 12=z/100 12 x 100=z z=1200 (and you plug in the % sign at the end) Hope that makes it clearr Link to comment Share on other sites More sharing options...

Ladybird Posted October 12, 2012 Author Share Posted October 12, 2012 Thank you!! It was simple in fact! they didnt put the %, now it make so much sense! THANKS Link to comment Share on other sites More sharing options...

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