Math Is Fun Forum

I don't think it makes a lot of difference for me, but sometimes I listen to classical music while doing some math or science work.

I guess it is and it isn't allowed.

A middle or high school science teacher gave his students this scenario: you’re standing by a tall building, and you need to find out about how tall it is. All you have available is a barometer. How can you use that to find out how tall the building is?

The “proper” answer, of course, was to measure the pressure on the ground, and at the top floor (or roof, if you could get to it) of the building, and use the formula for air pressure reduction by altitude to get the altitude of the roof and thus height of the building.

But one of his students decided to “smart off” and said, “Drop the barometer from off the top of the building, and time how long it takes to hit the ground. Plug that into the formula for gravitational acceleration.”

There problems are often referred to as "work word problems". Some of what I will post is advice from http://gmatclub.com/forum/work-word-pro … 87357.html.

I highly recommend you checkout the following websites as well for more information and practice
http://gmatclub.com/forum/work-word-pro … 87357.html

http://www.purplemath.com/modules/workprob.htm

There is a somewhat general way of solving these problems. However, do not go about these problems trying to remember some formula. Once you understand the logic underlying the above steps, you will have all the information you need to solve any similar word problem.

STEP 1: Calculate how much work each person/machine does in one unit of time (could be days, hours, minutes, etc).

How do we do this? Simple. If we are given that A completes a certain amount of work in X hours, simply reciprocate the number of hours to get the per hour work. Thus in one hour, A would complete

of the work. But what is the logic behind this? Let me explain with the help of an example.

Assume we are given that Jack paints a wall in 5 hours. This means that in every hour, he completes a fraction of the work so that at the end of 5 hours, the fraction of work he has completed will become 1 (that means he has completed the task).

Thus, if in 5 hours the fraction of work completed is 1, then in 1 hour, the fraction of work completed will be (1*1)/5

STEP 2: Add up the amount of work done by each person/machine in that one unit of time.

This would give us the total amount of work completed by both of them in one hour. For example, if A completes

of the work in one hour and B completes

of the work in one hour, then TOGETHER, they can complete

of the work in one hour.

STEP 3: Calculate total amount of time taken for work to be completed when all persons/machines are working together.

The logic is similar to one we used in STEP 1, the only difference being that we use it in reverse order. Suppose

. This means that in one hour, A and B working together will complete

of the work. Therefore, working together, they will complete the work in Z hours.

Good luck on your exam!

Thanks for your opinion, mathaholic.

I am sure most people here do not know what that first sentence means. If no one knows what it means, there is no need to post it on a primarily English speaking forum.

As I have already stated, some of these rules should be taken as guidelines and be enforced with leniency. A few common words (such as "Bonjour") here and there are not a breach of rule #1.

They allow that because there may be some uses for multiple accounts there and they do not have time to attend to requests for sibling accounts. Therefore, they may allow multiple accounts.

According to bobbym, bumping isn't allowed right now in the first place. In my opinion, one bump/no posts for one day is fair.

Once again, these rules should be taken not for word by word. If someone here says that they are in first grade and ask that question, someone would quickly answer it. The thing is, after a few times, that person would be referred to a very useful tool called calculator or google (since it has a built-in calculator).

It is very, very likely that such a proof has some mathematical fallacy. Yet again, these rules should not be taken word by word. If someone comes here and says they have a proof of 1 + 1 = 1 and they ask us to critique it, that is absolutely fine. If A.R.B comes in here posting speculative nonsense, their thread should be closed or deleted.

If anyone with such a ridiculous claim is correct, then everything from Phythagoras to the Fundamental lemma being proved is wrong. That person would immediately be hailed as the world's greatest mathematician etc. That is very unlikely and outside the capacity of any online forum.

Not at all, thanks for your perspective.

I wasn't taking about you and Amrita, of course.

I would want this forum to shut down before becoming as contest oriented and stricly moderated as AoPS.

You're welcome.

Hi, you are wrong. In the denominator it should be 2a which is 6 and in the numerator it is b not a plus or minus sqrt 49.

I meant only something very common, such as "what is a derivative?"

As for rule 18, I am sure you do not want anyone coming in here saying they proved Fermat's Last Theorem or proved that the theory of special relativity is nonsense, and then invent physics or mathematics to support their cause.

No, I haven't. I will try it later.

I like Chrome.