In a certain company, if 75% of the employees usually use a

Question

In a certain company, if 75% of the employees usually use a laptop, what percent of the employees usually use a PDA (Personal Digital Assistant)?

(1) 60% of the employees who usually use a laptop also use a PDA.
(2) 90% of the employees who usually use a PDA also use a laptop.

Bunuel · Accepted Answer

In a certain company, if 75% of the employees usually use a laptop, what percent of the employees usually use a PDA (Personal Digital Assistant)?

Assume there are total of 100 employees. Given: {Laptop users}=75. Question: {PDA users}=?

(1) 60% of the employees who usually use a laptop also use a PDA --> 0.6*{Laptop users}={Those who use both} --> {Both}=0.6*75=45. Not sufficient.

(2) 90% of the employees who usually use a PDA also use a laptop --> again {Both}=0.9*{PDA users}. Not sufficient.

(1)+(2) {Both}=45=0.9*{PDA users} --> {PDA users}=45/0.9=50. Sufficient.

Answer: C.

muralimba · Answer

subhashghosh · Answer

(1)

0.6 L Have PDA

So 0.6 * 75 Have both = 45 Have both

Not Sufficient, we don't know P

(2)

0.9P have laptop

Not Sufficient, we don't know P

(1) and (2)

0.9P = 45

=> P = 50

Answer - C

Spidy001 · Answer

1. Not sufficient .

here we have laptop only , laptop & pda . still not enough to find out pda .

2. Not sufficient.

we know that 90 % of pda user also use laptop . not enough to find out pda.

together we have

45E/100 = (90/100) PDA. enough to find pda interms of employees.

Answer is C.

anishashastri · Answer

I know this thread has been inactive for a while but if anybody could help solve my query it would be great.

See if you are assuming that 100 employees are there then
75% use laptops so 75 employees
1) 60%(75) use both so 45 employees
so by using the principle of sets 100= 75 + P -45
hence P=70
2)100=75 + P - (90/100)*P
solve this also and you'll get P
So the correct answer should be 'D' right?

Bunuel · Answer

{Total} = {Laptop} + {PDA} - {Both} +  {Neither} . So, you'll have one more variable in each statement thus you won't be able to solve.

Next, if you solve 100=75+P-0.9*P you'll get P=250, which does not make sense.

And finally,  on the GMAT, two data sufficiency statements always provide TRUE information and these statements never contradict each other  but from 100=75+P-45 you get  P=70  while from 100=75+P-0.9*P you get  P=250 , which cannot happen on the GMAT.

Hope it's clear.

anishashastri · Answer

Hi,
Appreciate the response. I was under the impression that if nothing has been given about the   part you can ignore it, anyway thank you! I get it now!

jlgdr · Answer

Hi Bunuel, for OS questions in DS. What is the best practice? I have tried different approaches but always have found drawing one matrix per statement the easiest. Every matrix would contain only the information provided in the question stem and stating clearly what I need to find. In worst case, I would have to draw 3. As a matter of fact, this is often the case. I find it that it can be a bit time consuming and was wondering if you suggest any other approach that could be at least as precise and error-free vs. using this approach
Thanks
Cheers
J

Bunuel · Answer

There are 3 approaches to tackle 2 overlapping sets problems:
1. Double-set matrix.
2. Venn diagram.
3. Formulas (as in this question).

Which one to choose depends on the problem and your personal preferences.

jlgdr · Answer

There are 3 approaches to tackle 2 overlapping sets problems:
1. Double-set matrix.
2. Venn diagram.
3. Formulas (as in this question).

Which one to choose depends on the problem and your personal preferences.[/quote]

Thank you for pointing that out. I agree that they fit different questions indeed and I have used all of them.
Now strictly for Double-Set matrix problems in DS
Is it the normal practice to draw three matrixes, one for the initial information given, one adding the info on Statement 1
And then a third one only adding info on Statement 2 (which you can then use if 1 and 2 are needed) ?
I find it a bit time consuming but proves to be safer, just wondering if you and other people around here do it this way

Cheers
J

srik9999 · Answer

Can anyone help me out with this problem using the double matrix technique. Thanks in Advance

Bunuel · Answer

Here you go: Untitled.png Hope it helps.

Fanja91 · Answer

I've written the following message for myself when studying, please ignore it as I realized it was far from well written.

Alright. We've got a few possibilities.

Let's name Laptop L and PDA P, B for both and N for neither.

L P B N = 4 possibilities.

Given is that 75% uses a laptop.

Statement 1: 60% of L also uses P. We've now got our B. 0.75*0.6.

Can we find out the percentage of PDA users from this?

We need B+P to answer that question. So no, we do not have the answer yet. Insufficient.

Statement 2:
90% who uses a PDA also uses a laptop. This tells us that 0.9*x uses a PDA. But we do not know as of now how big the "Both" part is.

But together with statement 1 we get:
0.9*x=0.75*0.6=0.45 x=0.5 So we know now that 50% uses a PDA.

Answer: C

This could probably also have been solved by a probability tree.

bumpbot · Answer

Automated notice from GMAT Club BumpBot: 

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

 This post was generated automatically.

In a certain company, if 75% of the employees usually use a

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Data Sufficiency (DS) Questions

In a certain company, if 75% of the employees usually use a

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards