Let C and J be their averages respectively for the 10 weeks.
Then the total number of books each reads for the 10 weak period is 10C and 10J respectively.

The question: Is C>J?
1) says 2C > 2J -5.
or C-J> -5/2. Since there are both negative and positive numbers > than -5/2 this is NOT SUFF. If C-J =-2,then J is greater. If C-J=2 then C is greater.

2) 5a-5b=3 where a and b are the averages of the last five weeks. This tells us that a>b. We need the average of the first five weeks for both and need to know whether one is greater than the other. We have to relate this info to stem to see whether we can figure out. Stem only gives us 10C and 10J where, C and J are 10 weak averages respectively.

So 10C-5a gives us the the total number of books Caro reads for first five weeks and 10J-5b gives number of books Jake reads for first 5 weeks. Lets find their respective averages

(10C-5a)/5=2C-a
10J-5b)/5=2J-b

call these e and f respectively

So 5e+5a=10C
5f +5b=10J

Subtracting second from first gives

5e -5f +(5a -5b) =10(C-J)
5e -5f +3 =10(C-J)

So 2 is not suff since we still have (C-J) as variable which is itself unknown.

Combining, we know C-J>-5/2, which cannot tell us whether e is greater or less than f. If C-J =-2, (which means C<J)RHS is negative, which in turn means f>e. If C-J = 2 (C>J) RHS is positive so e>f.

Choose E.

Thanks dtweah, however OA for this is A

Gmat09_5ALL wrote:Thanks dtweah, however OA for this is A

By what reasoning? Do you have it?

A doesn't look right to me.

A says 2C > 2J-5
take c = 20 and j =20 , it satisfies the above equation and the average # of books read is same.
if c=20 and j=21 then again the equation is true but the avg # of books read by c is less that books read by J. we can try another set of numbers c=21 and J=20, equation is still true and Avg # of books read by c is more than J.

IMO the answer should be E

dtweah wrote:Let C and J be their averages respectively for the 10 weeks.
Then the total number of books each reads for the 10 weak period is 10C and 10J respectively.

The question: Is C>J?
1) says 2C > 2J -5.
or C-J> -5/2. Since there are both negative and positive numbers > than -5/2 this is NOT SUFF. If C-J =-2,then J is greater. If C-J=2 then C is greater.

2) 5a-5b=3 where a and b are the averages of the last five weeks. This tells us that a>b. We need the average of the first five weeks for both and need to know whether one is greater than the other. We have to relate this info to stem to see whether we can figure out. Stem only gives us 10C and 10J where, C and J are 10 weak averages respectively.

So 10C-5a gives us the the total number of books Caro reads for first five weeks and 10J-5b gives number of books Jake reads for first 5 weeks. Lets find their respective averages

(10C-5a)/5=2C-a
10J-5b)/5=2J-b

call these e and f respectively

So 5e+5a=10C
5f +5b=10J

Subtracting second from first gives

5e -5f +(5a -5b) =10(C-J)
5e -5f +3 =10(C-J)

So 2 is not suff since we still have (C-J) as variable which is itself unknown.

Combining, we know C-J>-5/2, which cannot tell us whether e is greater or less than f. If C-J =-2, (which means C<J)RHS is negative, which in turn means f>e. If C-J = 2 (C>J) RHS is positive so e>f.

Choose E.

OA is indeed correct..

the question is asking is avg books of caroline/week -avg books of jacob/ week > 0?

Statement 1 gives us exactly that...
2* avg caroline/week - 2 avg books of jacob/week >5

therefore avg caroline - avg jacob > 5 therefore if it's greater than 5 it's definitely > than 0

hth

am getting E as well. whats the source?