Data Sufficiency

Hi I've searched the forum for htis question but it didn't show up. It deals with Ann depositing money into two simple interest earning accounts, A and B.

I answered incorrectly. Upon review, I think that just answer A would be enough but I don't understand why the correct answer is both are needed. My logic: If she deposited $100 into acct A and $300 into acct B (sample numbers based on fact 1), and you know the interests each account earns, B being greater than A, then wouldn't it be easy to find the interest difference between the two? It would be $4 . (8% of $300 = $24 and 5% of 100 = $20)

Why do we still need fact 2? We can still figure out the difference and that's all the question asks for.... Fact 2 adds some info about total interest but it's not absolutely necessary to find a difference.

Acct A
Let IA represent the interest from Acct A
IA=P(a)NR/100
IA=(P(a)*1*5)/100=0.05*P(a)
Acct B
IB=P(b)NR/100
IB=(P(b)*1* 8)/100=0.08*P(b)

Statement 1

P(b)=P(a)+200.........1
Insufficient

Statement 2

IA+IB=120
0.05*P(a)+0.08*P(b)=120...........2
Insufficient

Combining statement 1 and 2 we get

substituting 1 in 2 we get

0.05*P(a)+0.08(P(a)+200)=120
0.05*P(a)+0.08P(a)+16=120
0.13P(a)=104
P(a)=800
P(b)=P(a)+200=1000

the question is asking us to find IB-IA
IA=0.05*P(a)=40
IB=0.08*P(b)=80
IB-IA=40

Hence the ans is C...Let me know if you still have any doubts

Hi,
Thanks for the reply. I see what you did and how you calculated the values.

So it seems like they're saying there's a specific answer they're looking for. Me simply making up numbers based on fact I is the incorrect strategy?

I would still argue that my fake numbers will allow me to figure out the difference, however, I am not following the rules of this exam I guess. But I doubt semantics will get me far with the GMAT people!