Questions about the world of GMAT Math from other sources and general math related questions.
Jason.tuyj
Forum Guests
 
Posts: 35
Joined: Wed Dec 31, 1969 8:00 pm
 

Pls help to explain this prob

by Jason.tuyj Sat Sep 03, 2011 7:46 am

If n is the greatest positive integer for which 2^n is a factor of 10!, then n =
A. 2 B. 4 C. 6 D. 8 E. 10
mithunsam
Course Students
 
Posts: 74
Joined: Wed Dec 31, 1969 8:00 pm
 

Re: Pls help to explain this prob

by mithunsam Sat Sep 03, 2011 3:20 pm

10! = 1*2*3*4*5*6*7*8*9*10 = 1*2*3*(2^2)*5*(2*3)*7*(2^3)*9*(2*5) = 1*3*5*3*7*9*5*(2^8) [grouping all 2s together]

10! has eight 2s in it. Therefore n=8 is the answer.
tim
Course Students
 
Posts: 5665
Joined: Tue Sep 11, 2007 9:08 am
Location: Southwest Airlines, seat 21C
 

Re: Pls help to explain this prob

by tim Tue Oct 04, 2011 12:32 am

Thanks mithunsam!
Tim Sanders
Manhattan GMAT Instructor

Follow this link for some important tips to get the most out of your forum experience:
https://www.manhattanprep.com/gmat/forums/a-few-tips-t31405.html