I am not understanding the logic behind these types of questions.... How can i
get a value.
Please Help....
But please give me explanation of how to arrive to the answer..
Thanks.
GMAT Prep?? (Arithmetic Sequence) - Please HELP.
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statement 1 taken separately gives you the general term x(i) for i>1, so there is no way to deduct x(1).
statement 2 separately gives us clues only about x(5). No way to solve it either.
Taken together, we have:
x(i)=x(i-1)/2
and
x(5)=x(4)/x(4)+1
From these statements, we can say that x(4)+1=2, x(4)=1
Using the general term x(i)=x(i-1)/2, we can say that x(1)=2*x(2)=2*2*x(3)=2*2*2*x(4)=2*2*2*1=8
So using the statements separately, no solving.
Statements together, we have a solution.
statement 2 separately gives us clues only about x(5). No way to solve it either.
Taken together, we have:
x(i)=x(i-1)/2
and
x(5)=x(4)/x(4)+1
From these statements, we can say that x(4)+1=2, x(4)=1
Using the general term x(i)=x(i-1)/2, we can say that x(1)=2*x(2)=2*2*x(3)=2*2*2*x(4)=2*2*2*1=8
So using the statements separately, no solving.
Statements together, we have a solution.
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- Senior | Next Rank: 100 Posts
- Posts: 48
- Joined: Fri Aug 08, 2008 4:44 am
- Thanked: 4 times
- GMAT Score:750
It is clear that neither alone is sufficient. So try to solve the problem using both statements.
the problem is to find x(1).
You have 2 statements:
x(i)=x(i-1)/2
x(5)=x(4)/x(4)+1.
Both statements are true.
So lets calculate x(5) based on the first statement:
x(5)=x(5-1)/2=x(4)/2 --------------------------------- (1)
but x(5) is also = x(4)/x(4)+1------------------------- (2)
Acording to (1) and (2), we have the following equation:
x(4)/2=x(4)/x(4)+1. Divide the equation by x(4).
1/2=1/x(4)+1
x(4)+1=2
x(4)=1.
So we know x(4).
From the first statement,
x4=x3/2 => x3=2*x4
x3=x2/2 => x2=2*x3=2*2*x4.
x2=x1/2 => x1=2*x2=2*2*2*x4.
x4=1, so x2=2*2*2*1=8.
So using both statements, we can solve this problem.
Hope i was clear enough, I'm not very good at explaining stuff.
the problem is to find x(1).
You have 2 statements:
x(i)=x(i-1)/2
x(5)=x(4)/x(4)+1.
Both statements are true.
So lets calculate x(5) based on the first statement:
x(5)=x(5-1)/2=x(4)/2 --------------------------------- (1)
but x(5) is also = x(4)/x(4)+1------------------------- (2)
Acording to (1) and (2), we have the following equation:
x(4)/2=x(4)/x(4)+1. Divide the equation by x(4).
1/2=1/x(4)+1
x(4)+1=2
x(4)=1.
So we know x(4).
From the first statement,
x4=x3/2 => x3=2*x4
x3=x2/2 => x2=2*x3=2*2*x4.
x2=x1/2 => x1=2*x2=2*2*2*x4.
x4=1, so x2=2*2*2*1=8.
So using both statements, we can solve this problem.
Hope i was clear enough, I'm not very good at explaining stuff.