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2^x - 2^(x - 2)
= 2^x - (2^x / 2^2)
= (2^2 / 2^2) * 2^x - (2^x / 2^2)
= 2^2 * (2 ^ (x - 2)) - 2^(x - 2)
= 2^(x - 2) (2^2 - 1)
- by jimmylow
Sun Jan 04, 2009 1:30 am- Forum: Problem Solving
- Topic: 3 Problems from the GMAT Prep Program
- Replies: 13
- Views: 6221
Thks Zipper, Dana and Raja for simplifying third problem. Always good to see alternative (quicker) solutions 
- by jimmylow
Sat Jan 03, 2009 8:27 am- Forum: Problem Solving
- Topic: 3 Problems from the GMAT Prep Program
- Replies: 13
- Views: 6221
Yes, DanaJ is right about this one. Although I got B as the answer, I missed out the constraint that n < 200.DanaJ wrote: There could be more, but watch out: the next positive prime factor after 5 is 7 and 30*7 = 210, which is greater than 200. Therefore there are exactly 3 positive prime factors in n.
- by jimmylow
Sat Jan 03, 2009 8:22 am- Forum: Problem Solving
- Topic: 3 Problems from the GMAT Prep Program
- Replies: 13
- Views: 6221
This question appeared in Official Guide for GMAT Review 11th Ed (Orange) pg 186 Q249 "If n is a positive integer less than 200 and 14n/60 is an integer, then n has how many different positive prime factors?" a) two b) three c) five d) six e) eight Ans: B 14 * n / 60 = (7 * 2 * n) / (3 * 5...
- by jimmylow
Sat Jan 03, 2009 7:59 am- Forum: Problem Solving
- Topic: 3 Problems from the GMAT Prep Program
- Replies: 13
- Views: 6221
Let me attempt this one: "If 2^x - 2^(x-2) = 3(2^13), what is the value of x?" a) 9 b) 11 c) 13 d) 15 e) 17 [Working] 2^x - 2^(x-2) = 3 (2^13) = [(2^2)(2^x) - (2^x)] / (2^2) = 3 (2^13) = 2^(2+x) - 2^x = 3 (2^13) (2^2) <--- this is done by multiplying 2^2 both sides 3 = 2^2 - 2^0 <---- anyt...
- by jimmylow
Sat Jan 03, 2009 7:13 am- Forum: Problem Solving
- Topic: 3 Problems from the GMAT Prep Program
- Replies: 13
- Views: 6221