exponents prob 2....

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willbeatthegmat: Senior | Next Rank: 100 Posts; Posts: 71; Joined: Sat Sep 20, 2008 5:48 am; Thanked: 5 times

by willbeatthegmat » Mon Feb 09, 2009 2:30 pm

If 5^x=y, what is x?
a)y^2= 625
b)y^2= 15625

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Source: Beat The GMAT — Problem Solving | Mon Feb 09, 2009 2:30 pm

sureshbala: Master | Next Rank: 500 Posts; Posts: 319; Joined: Wed Feb 04, 2009 10:32 amFollowed by: 9 members; Location: Delhi; Thanked: 84 times

by sureshbala » Mon Feb 09, 2009 3:12 pm

Could you please check the question (or the source) once again. Because in GMAT DS normally you will not have two contradictory statements.

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willbeatthegmat: Senior | Next Rank: 100 Posts; Posts: 71; Joined: Sat Sep 20, 2008 5:48 am; Thanked: 5 times

by willbeatthegmat » Wed Feb 11, 2009 5:42 am

sorry...statement 2) y^3 = 15625

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marcusking: Master | Next Rank: 500 Posts; Posts: 106; Joined: Wed Feb 04, 2009 6:09 am; Location: Louisville, KY; Thanked: 8 times

by marcusking » Wed Feb 11, 2009 6:22 am

a.) Given that the sqrt(625) is 25
that gives us that 5^x = 25 and thus x = 2
A is sufficient

b.) Given that 625 is 25^2 then 625 * 25 = 15625 and we know that
that gives us 5^x = 25 and thus x = 2
B is sufficient

So Each statement alone is sufficient

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willbeatthegmat: Senior | Next Rank: 100 Posts; Posts: 71; Joined: Sat Sep 20, 2008 5:48 am; Thanked: 5 times

by willbeatthegmat » Wed Feb 11, 2009 6:34 am

that looks very simple n obvious...wat if y = -25....wat wud b d value of x in stat 1

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cjb: Senior | Next Rank: 100 Posts; Posts: 66; Joined: Fri Oct 31, 2008 2:41 pm; Location: London, UK; Thanked: 5 times; GMAT Score:770

by cjb » Wed Feb 11, 2009 6:53 am

marcusking wrote:a.) Given that the sqrt(625) is 25
that gives us that 5^x = 25 and thus x = 2
A is sufficient

But (-25)^2 also equals 625.

Not sure what that would mean in this case, as I don't know how to solve

5^x = -25

Nonetheless, I would answer B, not D.

80% of success is showing up -- Woody Allen

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marcusking: Master | Next Rank: 500 Posts; Posts: 106; Joined: Wed Feb 04, 2009 6:09 am; Location: Louisville, KY; Thanked: 8 times

by marcusking » Wed Feb 11, 2009 6:56 am

willbeatthegmat wrote:that looks very simple n obvious...wat if y = -25....wat wud b d value of x in stat 1

hmmmm........
I don't think this is possible. Since the base of the number is 5 and not -5 I don't think there is any power you can raise it to that would cause it to be -25. If we try raise it to any negative root we end up getting a decimal. If we try and raise it to any fraction or decimal of a power we still get a positive number.

Anyone else

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