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Gmat Prep practice test 2 Quant question

Expert replies
Source: — Problem Solving |

Fab_Vr6 wrote:What is the greatest prime factor of 4^17 - 2^28

answers choices are: 2, 3, 5, 7, 11
4^17 - 2^28
= 4^17 - 4^14
= 4^14(4^3 - 1)
= 4^14 * 63
= 4^14 * 3 * 3 * 7

7 is the greatest prime factor
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by Fab_Vr6 » Sat Jun 02, 2007 4:27 pm
jayhawk,

I don't quite get this part:

= 4^14(4^3 - 1)
= 4^14 * 63
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by jayhawk2001 » Sun Jun 03, 2007 6:54 am
Fab_Vr6 wrote:jayhawk,

I don't quite get this part:

= 4^14(4^3 - 1)
= 4^14 * 63
4^3 = 64. 64-1 = 63
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