Problem Solving

I am trying to do these questions by employing the Double MAtrix Charts. I do not want THE VENN DIAGRAM WAY. ANy help?

The first one is not that straight forward, but is much easier to view when you break down the information.

You can draw a chart with R NR for Russian, No Russian and F NF for French, no French.

The intersection of F and R will be your .10 figure (10 percent)

The intercection of NR and NF will be your .20 figure.

Then, you enter x for the total.

Now, you are told that 32 DO NOT speak Russian, so let's put that number in the total for NR.

You are also told that 20 speak French. So, enter 20 for the total of F.

Now, you can plug in a number for x, and it is better to start with a nice number like 120 or 150. I would usually start with 120, which would then show me whether I should work up or down, but I will start with 150, to prove my point.

150 - 20 = 130 total for people who do not speak French.

.20(150) = 30 who speak nether language, which leaves you with 2 who speak French but no Russian and 18 who speak both.

Now, is 10 percent of 150 = 18? No.

So, try the same thing with 120, now.

120 - 20 = 100 who speak no French at all.

.20(120) = 24 who speak neither Russian nor French, which leaves you with 8 who speak French but no Russian and 12 who Speak both.

Is 12 10 percent of 120? YES!

That is your answer.

This problem took me a little over 2 minutes to solve. I am sure that there is a faster way, but this is how I would solve it on the exam.

For the second one, I would draw a Venn diagram at once to assist me in arranging the information.

I always start working from the middle. So, put 500 for the number of people who read both.

Now, you are told that this is half of those who read only B, so B will be 250; put this in your diagram.

Now, you are told that A is twice the number who read B.

I initially started to calculate for 250 and get 2(250), HOWEVER, when I looked back at my diagram, I realized that I was starting to head in the wrong direction.

250 represents the number of people who read ONLY B, not ALL of the people who read B.

Then, I realized that the 500 + 250 = 750 which represents ALL of the people who read B.

Then:

2(750) = 1500, ALL of the people who read A.

To get ONLY A, you just 1500 - 500 = 500.

There's no need to guess numbers here... definitely too time consuming.

Once you set up the data as AleksandrM suggests simply fill in some of the blanks:


|F |NF |
R |.1T | |
NR| |.2T | 32
|20 | | T


|F |NF |
R |.1T |.8T-20 | *
NR| |.2T | 32
|20 | T-20 | T


Now check out where I put the *.

We know this has to equal .1T + .8T -20 and also T-32

So:

T-32 = .1T +.8T -20
.1T = 12
T = 120

AleksandrM wrote:The first one is not that straight forward, but is much easier to view when you break down the information.

You can draw a chart with R NR for Russian, No Russian and F NF for French, no French.

The intersection of F and R will be your .10 figure (10 percent)

The intercection of NR and NF will be your .20 figure.

Then, you enter x for the total.

Now, you are told that 32 DO NOT speak Russian, so let's put that number in the total for NR.

You are also told that 20 speak French. So, enter 20 for the total of F.

Now, you can plug in a number for x, and it is better to start with a nice number like 120 or 150. I would usually start with 120, which would then show me whether I should work up or down, but I will start with 150, to prove my point.

150 - 20 = 130 total for people who do not speak French.

.20(150) = 30 who speak nether language, which leaves you with 2 who speak French but no Russian and 18 who speak both.

Now, is 10 percent of 150 = 18? No.

So, try the same thing with 120, now.

120 - 20 = 100 who speak no French at all.

.20(120) = 24 who speak neither Russian nor French, which leaves you with 8 who speak French but no Russian and 12 who Speak both.

Is 12 10 percent of 120? YES!

That is your answer.

This problem took me a little over 2 minutes to solve. I am sure that there is a faster way, but this is how I would solve it on the exam.

resilient,

believe me the double chart method (if I am not mistaken, you are referring to the MGMAT method) is so nice and easy.

How ever, If you look at the Q, it does not fit that double matrix method

AFAIK, the problem needs to meet certain requirements to use the DM method. Look at other problems you solved with DM method. Aren't they quite different? The second Q differs from the other Q's which can be solved using DM in that it does not involve !A and !B but says only A and only B


Edit: I did not look at the first Q as I thought it was a repost from last night.

Please find attachment with DM method for the first Q

yes you are right. I am an mgmat student and im using an 800score exam. the exam is a bit tougher and charts dont work here. Regardless for exam day I am using the charts. THey are much more straightforward and the charts do the work for you. thanks

For some reason backsolving escapes me during the heat of an exam. IN fact I try to be the hero and plug the whole down by straightforward math. I t is clear to see with such great efforts of the contribuotrs that backsolving works great here. THanks a lot guys.

Its very easy to talk about back solving. Don't worry. It only comes with practice by looking at answers more than trying to solve the problem. In one way, That means our fundamentals are not strong enough.

Implementing that is very difficult for normal test takers. Gurus like Stuart and Ian can do it with ease. I doubt they will end up back solving in the first place. Back solving to me is like hindsight

Question 1.
For those who want to use Venn Diagram.
View the attachment.

On similar lines

Question 2.

Using the data

Both = 500

B =250

in A+Both=2(B + Both)

we get A = 1000.

Kamu,
thanks for the Venn, but plugging in your values, I get 60 (which was my original answer when trying to work out this problem).

Could you please go through your working (inserting the values for I, II, III & IV) again, as I'm becoming increasingly confused with Venns...

Many thanks

Baldini wrote:Kamu,
thanks for the Venn, but plugging in your values, I get 60 (which was my original answer when trying to work out this problem).

Could you please go through your working (inserting the values for I, II, III & IV) again, as I'm becoming increasingly confused with Venns...

Many thanks

try this
F+R+.2t-.1t=t... you will get the answer

Logic should be F+R-B+N=T

Would this be a possible way of solving the problem (or is it just fluke).
32 people speak no Russian.
Total = FR + RU + Neither - FR&RU
Therefore RU = FR + Neither

We know that 20 speak French and we know that 10% of the Total speak Neither thus:

RU = FR + Neither
32 = 20 + 0.1T
12=0.1T
T=120

thanks