A manufacturer produced x percent more video cameras in 1994

[Luci]

Can anyone explain this? I think to solve it we first need to discover the value of X and then the value of Y. But how can we solve for each two values with just one equation? That is why I thought it was C, because we had two equations and two variables. Or we dont need to solve for them separately???




One more thing, dont you think the quant part of GMATPREP 2 is much much easier than the quant part of GMATPREP 1??? Or maybe is that I have improved my quant skills since I did the first exam ;-p

I got a 49 with 8 errors four of which were stupid mistakes (specially three of them).

Thanks

[GMAT 2007]

Luci - this one is tricky, and it lies in the question stem itself.

No. of Video Cameras produced in 1993 = 1000
Assume 'a' be the increase in no. of video cameras in 1994,

So x = (a/1000)*100 or a = 10x

Similarly assume b be the increase in no. of video cameras in 1995,

So y = (b/(1000+10x))*100 or b = ((100+x)/10)*y

Now total no. of video cameras in 1995 = 1000 + a + b = 1000 + 10x + ((100+x)/10)*y...(1)

Solving (1)

10(100+x) + ((100+x)/10)*y

= (100+x)(10+y/10) = (100+x)(100+y)/10 = 10000+10(x+y) + xy/10 = 10(1000+(x+y)+xy/100)

Now statement (2) gives us the value of the expression (x+y)+xy/100. Hence it is sufficient.

GMAT 2007

[Luci]

Amazing explanation GMAT 2007. Thanks a lot. Although I think it is a very tough problem, I dont think I will be able to solve it in 2 minutes. Not because the logic of the question stem, which is brilliant how you did it, but all the factoring you have done seems too tough to me. This is one of those to try a good guess and keep going I think, :-).

[Guest]

We could also do this problem the following way:

1993 = 1000 video cameras
1994 = 1000*(1+x/100)
1995 = 1000*(1+x/100)(1+y/100)

group the equation for 1995
1995 = 1000*(1+x/100+y/100+xy/10,000)

Evaluate the statements

Statement 1) This is insufficient because we need the values for x and y

Statement 2) is the further simplified from the equation we have x+y+xy/100=9.2, which can be simplified to fit our rephrased equation

1995 = 1000*(1+x/100+y/100+xy/10,000) = 9.2
1+x/100+y/100+xy/10,000=.0092 (divide both sides by 1000)
x/100+y/100+xy/10,000=.0092-1=.9908 (subtract 1 from both sides but ignore the negative sign because you cannot sell negative video cameras)
x+y+xy/100=99.08 (after multiply throughout by 100)

[RonPurewal]

Luci - this one is tricky, and it lies in the question stem itself.

No. of Video Cameras produced in 1993 = 1000
Assume 'a' be the increase in no. of video cameras in 1994,

So x = (a/1000)*100 or a = 10x

Similarly assume b be the increase in no. of video cameras in 1995,

So y = (b/(1000+10x))*100 or b = ((100+x)/10)*y

Now total no. of video cameras in 1995 = 1000 + a + b = 1000 + 10x + ((100+x)/10)*y...(1)

Solving (1)

10(100+x) + ((100+x)/10)*y

= (100+x)(10+y/10) = (100+x)(100+y)/10 = 10000+10(x+y) + xy/10 = 10(1000+(x+y)+xy/100)

Now statement (2) gives us the value of the expression (x+y)+xy/100. Hence it is sufficient.

GMAT 2007

well played.

[kamran_veg45]

It's data sufficiency, all you need is:

x + y + xy/100 = 9.2

since video cameras in 1995 equals:
1000*(1+x/100)(1+y/100)
1000*(1 + y/100 + x/100 + xy/10,000)

you factor out a 1/100 from the equation and you are left with:
1000/100*(100 + (y + x + xy/100))

Now, knowing the information we have from (2) => x + y + xy/100 = 9.2:
10(100+9.2) = 1092

Therefore, B is sufficient and A is completely useless (as A does not tell us anything about x and y).

I don't think you need to do all that factoring nonsense LOL..and you can do this question in under a minute! And I agree with Luci, questions in the 2nd gmat prep were a lot easier, I thought.

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I think the guest confused himself/herself as he did all the intricate calculations, because it's clearly mentioned in the question that x + y + xy/100 = 9.2 and the guest comes out with the answer: x + y + xy/100 = 99.08 ! He/she, for some reason, claimed that 1000*(1+x/100+y/100+xy/10,000) = 9.2, which is WRONG! The portion inside the bracket equals 9.2 as explained above! According to the guest, the video cameras in 1995 equal 9.2...WRONG! Please read carefully.

Also, GMAT 2007, please have a look at your factoring! There is a mistake in the underlined portion in between the bold steps:
= (100+x)(10+y/10) = (100+x)(100+y)/10 = 10000+10(x+y) + xy/10 = 10(1000+(x+y)+xy/100)

The 1/10 outside the bracket applies to the entire bracket, so the 10000+10(x+y) + xy/10 should actually be 1000+10(x+y) + xy/10 and the final equation should actually be: 10*(100 + (y + x + xy/100)) as mentioned earlier!

Besides that, all is correct :)

-Hope this helps!

[RonPurewal]

one other thing about this problem:

statement (2) is WEIRD.
really weird.
so weird that it can't possibly be a randomly generated statement.

GUESSING GUIDELINE:
if you see a really weird, really elaborate looking statement, it's very likely to be "sufficient".
here's the rationale: if you look at statement (2) to this problem, it's clear that it has been very deliberately crafted to do ... something; it's obviously not a statement that has been made up at random (unlike statement (1), which could be random). most probably, that "something" will make the statement sufficient.

to see another example of "weird statements are usually sufficient", take a look at data sufficiency #120 in the 12th edition OG. or, if you have the 11th edition, look at #153.