Liam is pulled over problem 4th Ed. Word Trans page 171

[a.sarwari]

Liam is pulled over for speeding just as he is arriving at work.He explains to the police officer that he could not afford to be late today, and has arrived at work only four minutes before he is to start. The officer explains that if Liam had driven 5mph slower for his whole commute, he would have arrived at work exactly on time. If Liam's commute is 30 miles long,how fast was he actually driving?(Assume that Liam drove at a constant speed for the duration of his commute.)

The strategy guide does NOT go over how they get from the set up to setting the times equal to each other 30/r = [(30/(r+5))+(1/15)].

I understand how the guide gets to this point BUT I need someone to explain the rational behind setting the times equal to each other.

What in the problem prompts this set up? It will be easier for me to remember if I understand the logic behind it.

Thank you in advance!

[StaceyKoprince]

Good question! I completely agree that we learn better when we understand the logic behind something.

I do want to get an equation at some point so that I have something to solve. The two timeframes actually don't equal each other at this point - while speeding, Liam gets there 4 minutes early, but if he hadn't sped, then he'd have gotten there exactly on time. So what do I need to adjust in order to make those two timeframes equal?

Hmm. Speeding took 4 minutes less than not speeding. How would i make those two times equal? Add 4 minutes to the faster time - the speeding time. Then that'll equal the slower time - the time it would've taken when NOT speeding.

so I've got:
non-speeding time = speeding time + 4 minutes
Oh, but how annoying - the speeding and non-speeding times were given in terms of hours, not minutes (because the rates were miles per hour). So I can't just use +4. I have to convert minutes to hours.

4m * (1h / 60m) = (1/15) hour
so I'll use 1/15 in the equation instead.

Does that make more sense now? :)

[uzmail]

I will thank you for a.sarwari. You guys are awesome-Stacey, Tim, Ron and everyone else.

I wonder if one can reach to 700+ level by just reading your posts and comments on the website because it seems like you guys have it all that takes to get there.
MGMAT is being really helpful in my 15 day boot camp preparation (10 hrs a day) :)

[RonPurewal]

Ten hours a day is way too much. You're almost certainly deriving no benefits whatsoever from the last half of that time.

[uzmail]

I think you're right, Ron. My CAT tests results are not improving (actually getting lower) and I'm spending way too much time reviewing single math Qs after some time.

I thought I was good at Math, but I guess I didn't realize how rusty I'd gotten+Gmat math is different. Clicking about 7-8 Qs at the end as fast as possible before time is up.

Anyway, I think I need to alter my prep duration and strategy at this moment...

[RonPurewal]

I think you're right, Ron.

This is not an issue of "Ron is right"/"Ron is wrong". This is a fundamental issue of human neuroplasticity. As a normal adult, you are INCAPABLE of learning for that many hours in a day.
Or even close.
Max is about 4 hours or so--and that's only if the rest of your life is essentially a stress-free Shangri-La of tranquil contentment. If you're stressed or tired, it's less than that.

Note that I'm talking about learning, not about doing. Given enough motivation--and, perhaps, nootropic or stimulant drugs--people can obviously DO things (task execution) for much longer than that. But, learning? Nah.

If you were a small child, of course, this would be a whole different story.

[RonPurewal]

My CAT tests results are not improving (actually getting lower)

Remember that CAT results have a standard deviation of 40-50 points, and probably a little more near the top and bottom of the scale.

This means that, if you could split yourself into two selves and send both selves to take a test at the same time, the two scores would differ on average by 50-60 points. (I'll spare you the statistical analysis, but two random points on a bell curve differ by an average of about 1.1-1.2 times the standard deviation.)

In other words, almost all of the score variations you see are random noise.
Honestly, the score is the least important part of your CAT exam. The value lies in ...
... experiencing the rhythm of a full test during the practice exam,
... review and diagnosis afterward.

[RonPurewal]

and I'm spending way too much time reviewing single math Qs after some time.

Make sure that you always allow at least a few days to pass before reviewing problems.

DO NOT, EVER, do a "thorough" review of a problem right after finishing it. This is 2 kinds of bad:
1/ You're denying yourself the experience of dealing with constant uncertainty, which is an integral element of the real exam.
Remember, there are 37 consecutive math problems and 41 consecutive verbal problems——and you'll never be able to "check your work".
If you're stopping after every practice problem, you'll be completely unprepared for this experience... which may well explain why you aren't finishing tests.

[RonPurewal]

Clicking about 7-8 Qs at the end as fast as possible before time is up.

Don't make time management more complicated than it actually is.

There are only 3 elements to time management:

1/
Be brutally, uncomfortably honest with yourself about WHEN YOU ARE STUCK.

2/
If you are stuck, STOP WHAT YOU'RE DOING.
If you can think of something else, try it.

3/
Don't try the same type of approach more than once. If it's SC, don't keep staring at the same words if you didn't figure them out the first time around.

That's it. Thinking explicitly about minutes/seconds is necessary only if you lack the self-discipline to do these 3 things.

#1 is the biggest problem, because, for years and years and years, your formal education biased you against it.

See, in school, people get Partial Credit. Which is pretty much THE worst thing you can do to a child's mind.
• Partial Credit teaches people that self-honesty and caution—"I honestly don't know how to do this"—are bad things.
• Partial Credit teaches people that doing random "work" with no goal whatsoever is a GOOD thing. It actively rewards this behavior.

As a result of years and years of Partial Credit, you've acquired instincts that would be positively ridiculous anywhere outside of school. (If you were building furniture and got stuck, would you just nail random pieces of wood together and hope for Partial Credit? You see my point.)

So, you need to import your (non-dysfunctional) instincts from the real world.
Imagine that you're driving somewhere, and you're already late. You get lost... even somewhat lost.
What do you do?
You stop driving. You pull over and solicit help (from your GPS, friends, whatever). But, whatever the heck you do, you most certainly don't drive around in random directions, hoping that, by some miracle, you'll find your destination.

Same thing here. If you don't have a VERY good idea of where you're going, you need to stop.

This is 100.00000% of time management. You don't need to be "fast", not at all. (In fact, most students could benefit from working more slowly.)

[RonPurewal]

Oh, and, last but not least, the numbers that matter are the numerical scores.

The percentiles, in particular, are pretty much irrelevant, especially since they are now so skewed.
Almost half of ALL people taking the GMAT are now from other countries——and, of those individuals, the vast majority have an engineering/technical background of some sort. So, percentiles are now severely distorted.

For instance, you may have heard, once upon a time, that "80th percentile on both parts" was a good standard to use for applying to top schools.
OK, 10-15 years ago that was probably not terrible advice (though, even way back then, it still would have dissuaded some otherwise excellent candidates).

But, now? Ha... no.
GMAC updates current percentiles here:
http://www.mba.com/us/the-gmat-exam/gma ... -mean.aspx
Look at the quant chart. At this point in time, "80th percentile quant" means either 50 or 51. Even a 49 is below that cut-off now.
Obviously, not everyone at top b-schools is walking around with a Q50 or Q51. So, if anyone is still dispensing this advice ... well, now it's terrible advice. As I wrote above, once upon a time it may have had some currency... but certainly not now.