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tennis_nerd22
08-28-2008, 11:35 AM
........................

split-step
08-28-2008, 12:50 PM
Well, an integer multiplied by an integer will always give you an integer.
So if we take the first part to be 5 for all options , only option 1 gives the exponent part as an integer (10^5)

The other 2 have the exponent part as decimals.

Majortests.com fails.

Steady Eddy
08-28-2008, 03:11 PM
k so im doing some study questions for SAT cuz i have to take it soon.. and i dont understand the answer to this question:

"
9. If x is an integer, which of the following could be x³?

I 1.25 x 1017
II 12.5 x 10-12
III 0.125 x 10-12

A. I only
B. II only
C. I and II only
D. I and III only
E. II and III only

Correct Answer: D

Explanation:

We can shift the decimal points so that we get 125 and a power of ten. 125 is a cube. If the power to which ten is raised is divisible by 3, then that is also a cube.
For statement I we get 125 x 1015 (We have multiplied the 1.25 by 100 and so we must divide 1017 by 100 which means we subtract 2 from the power). For statement II we get 125 x 10-13, and for III we get 125 x 10-15. Only in the case of I and III is the power divisible by three.
"

http://www.majortests.com/sat/explain.php?exp=503031312439243436

It said if x is an integer, meaning a whole number? So that would mean the answer would be A, because the cube root of choice III is 5x10^-5 (or 0.00005). And that number is not an integer :|

Anyone have any ideas? I know this is a lame topic to start a thread about, especially on a tennis forum, but i need a good SAT math score lol cuz my english is ******
First of all, you should help out we readers by using the carrot "^" to indicate exponents. Then the first choice I. would read, 1.25 x 10^17. See? So we could make the first factor bigger by moving the decimal over two places, to compensate, we must move the decimal for the second factor over two places in the opposite direction. Then we get 125 x 10^15. This looks different, but has the same value as before. 125 = 5^3, and 10^15 = (10^5)^3, so each factor is an integer cubed, so the product is also a cube.

But for III. they make a mistake. This time we move the decimal over three places. So we re-write it as: 125 x 10^-15. 125 = 5^3 and 10^-15 = (10^-5)^3. But they're forgetting that 10^-5 is NOT an integer. We expressed it using integers, but it is 0.00001, clealy not an integer. Therefore the correct answer is A, not D.
(I don't like to quickly say that an answer guide is wrong. So I double-checked these on a calculator. Put them in a calculator one at a time, then take the cube root. If the cube root is an integer, then x could be an integer as well.)

persondudething
08-28-2008, 05:43 PM
wow, i took an extremely rigorous and comprehensive sat class this summer and have never seen a problem as hard as that....

tennis_nerd22
08-28-2008, 06:19 PM
First of all, you should help out we readers by using the carrot "^" to indicate exponents. Then the first choice I. would read, 1.25 x 10^17. See? So we could make the first factor bigger by moving the decimal over two places, to compensate, we must move the decimal for the second factor over two places in the opposite direction. Then we get 125 x 10^15. This looks different, but has the same value as before. 125 = 5^3, and 10^15 = (10^5)^3, so each factor is an integer cubed, so the product is also a cube.

But for III. they make a mistake. This time we move the decimal over three places. So we re-write it as: 125 x 10^-15. 125 = 5^3 and 10^-15 = (10^-5)^3. But they're forgetting that 10^-5 is NOT an integer. We expressed it using integers, but it is 0.00001, clealy not an integer. Therefore the correct answer is A, not D.
(I don't like to quickly say that an answer guide is wrong. So I double-checked these on a calculator. Put them in a calculator one at a time, then take the cube root. If the cube root is an integer, then x could be an integer as well.)

thanks for the explanation.

and about the exponents, i copy+pasted and wrote the thread really quickly and i had no idea that the ^'s were missing.. i guess i should have realized cuz on the actual website they were in superscript. sorry about that

wow, i took an extremely rigorous and comprehensive sat class this summer and have never seen a problem as hard as that....

really? lol that question was worded in a weird way but.. yea i hope i dont see it on the actual test lol

did u take the reading/writing too? like the SAT reasoning test?

Majortests.com fails.

haha i guess so.. iunno i found it a pretty helpful site. everyone makes mistakes i guess? haha

flynhawaiian
08-28-2008, 06:52 PM
realistically, it's not a hard question it's not even a math question honestly. It's a linguistics question. First off what is the definition of an integer? A whole number.

I 1.25 x 10^17
II 12.5 x 10^-12
III 0.125 x 10^-12

I) would yield a whole number
II) would yield NOT a whole number
III) would yield NOT a whole number

If you can use a calculator, simply type out:

1.25e17.

1 note to remember is that wrong answers count against you on this test o-o. I never learned that until I started taking the LSAT haha.

GL on the test :-)

persondudething
08-29-2008, 05:32 PM
tennis_nerd22,

pretty much all i did for 6 weeks was do sat problems. overall, the test is easy. the material is set at a level where most people can take it and do reasonably well. the math material is extremely easy. nothing past maybe algerbra and geometry. they get you with their tricks. see through them and you should do fine. english is a little tougher. writing is mostly grammar. if you knock the question section out of the park, you dont need a perfect essay grade to get an 800. for reading, one word; vocab! study your vocabulary words and your score WILL go up. of course reading comprehension is important but vocab is really big in the reading section.
hope that helped