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few DS and PS questions.. [#permalink]
20 Aug 2007, 10:18

hey guys! thanks soo much for looking at this post.. i know these questions are easy for you guys, but i would really REALLY appreciate help! i feel i am lacking the basics.. lol

For every integer K from 1 to 10 inclusive, the Kth term of a sequence is given by:
(-1)^k+1 (1/2^k)
If T is the sum of the first 10 terms in the sequence, then T is:

OK so i plugged in 1 and got 1/4.. but i dont understand why the answer is between 1/4 and 1/2.. bc if I plug in 10.. doesnt (-1)^11 give us -1??

What function is f(a+b)=f(a)+f(b) for all positive numbers a+b?

I just really forget how functions work! so if someone could help me out here, that be wonderful! the answer is F(x)=-3x

If the speed of X meters/sec. is equivalent to the speed of Y km/hr. what is Y in terms of X?

3600000x

18x/5

5x/18

6x/5

60x

Just confused as to the best approach to set this question up.

Thanks again for all your help!! i have the GMAT in 7 days.. and i am mildly stressing! LOL!

For every integer K from 1 to 10 inclusive, the Kth term of a sequence is given by:
(-1)^k+1 (1/2^k)
If T is the sum of the first 10 terms in the sequence, then T is:

The first term is (-1)^2(1/2) = 1/2
The second term is (-1)^3(1/2) = -1/4
The third term is (-1)^4(1/8) = 1/8
The fourth term is (-1)^5(1/16) =-1/16

So we have on our hands a geometric progression with sum of term given as S =a(1-r^n)/(1-r)

So a = 1/2, r = -1/2, n = 10. S = 1/2(1-(-1/2)^10)/(1+1/2). The term (-1/2)^10 is going to be very big, so the S is close to (1/2)/(2/3) = 1/3 which is between 1/2 and 1/4.