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EIV Guide 3 Page 122

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nyc.willchan
 Post subject: EIV Guide 3 Page 122
 Post Posted: Sun Jul 04, 2010 11:46 pm 
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Course Students


Posts: 3
Directly from the book:

If x=5 to the 20th power and y=5 to the 19th power, what is x - y, in terms of y?

(C) 4y

Here, we must connect the given values of x and y in some way. Since 5 to the 20th power = 5 * 5 to the 19th power, we can write x=5y. Now the target expression x - y can be rewritten as 5y-y=4y.

I do not understand why how 5*5 to the 19th power is the same as x=5y.
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adiagr
 Post subject: Re: EIV Guide 3 Page 122
 Post Posted: Mon Jul 05, 2010 12:32 am 
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Students


Posts: 89
nyc.willchan wrote:
Directly from the book:

If x=5 to the 20th power and y=5 to the 19th power, what is x - y, in terms of y?

(C) 4y

Here, we must connect the given values of x and y in some way. Since 5 to the 20th power = 5 * 5 to the 19th power, we can write x=5y. Now the target expression x - y can be rewritten as 5y-y=4y.

I do not understand why how 5*5 to the 19th power is the same as x=5y.



the question says:

x - y = 5^20 - 5^19

Take (5^19) common, the expression becomes:


5^19. (5 - 1) = 5^19 . 4

Now y = 5^19 .

so expression becomes 4y
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nyc.willchan
 Post subject: Re: EIV Guide 3 Page 122
 Post Posted: Mon Jul 05, 2010 3:21 am 
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Course Students


Posts: 3
I am sorry but I still do not understand what I asked earlier based on the explanation below after your first sentence:

"Take (5^19) common, the expression becomes:


5^19. (5 - 1) = 5^19 . 4

Now y = 5^19 .

so expression becomes 4y"

There are symbols, words, etc which I am not familiar with. ie Common? ie 5^19 - yes. What does the period after the 19 represent (in both instances on the second quoted line)?

Thanks for your help
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adiagr
 Post subject: Re: EIV Guide 3 Page 122
 Post Posted: Mon Jul 05, 2010 7:21 am 
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Students


Posts: 89
nyc.willchan wrote:
I am sorry but I still do not understand what I asked earlier based on the explanation below after your first sentence:

"Take (5^19) common, the expression becomes:


5^19. (5 - 1) = 5^19 . 4

Now y = 5^19 .

so expression becomes 4y"

There are symbols, words, etc which I am not familiar with. ie Common? ie 5^19 - yes. What does the period after the 19 represent (in both instances on the second quoted line)?

Thanks for your help



Will try to help.

5^19 means 5 raised to the power 19.

x.y means => x multiplied by y.

See expression is:

5^20 - 5^19

This can be written as: 5 .(5^19) - 1. (5^19)

Taking (5^19) out, we can write

(5^19) (5-1)

which is (5^19)(4)
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nyc.willchan
 Post subject: Re: EIV Guide 3 Page 122
 Post Posted: Mon Jul 05, 2010 2:51 pm 
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Course Students


Posts: 3
PERFECT! Now it makes sense. You factored both expressions out which in turn becomes y. That was the missing link. Again, thanks a lot for your help.
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tim
 Post subject: Re: EIV Guide 3 Page 122
 Post Posted: Thu Jul 08, 2010 1:46 pm 
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ManhattanGMAT Staff


Posts: 2242
Location: Southwest Airlines, seat 21C
thanks, adiagr..

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Tim Sanders
Manhattan GMAT Instructor
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