CHalkboard problem

A

Applz

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Bart is writing lines on a chalk board that is initially empty. It ordinarily takes Bart 50 minutes to cover the whole board; however, today, Nelson is erasing the board while Bart is writing. Nelson can erase the board in 90 minutes by himself. If they work simultaneously, how long will it be (in minutes and seconds) until the board is covered?
 
Applz said:
Bart is writing lines on a chalk board that is initially empty. It ordinarily takes Bart 50 minutes to cover the whole board; however, today, Nelson is erasing the board while Bart is writing. Nelson can erase the board in 90 minutes by himself. If they work simultaneously, how long will it be (in minutes and seconds) until the board is covered?
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Bart can cover - what fraction of the board in 1 minute.

Nelson can erase - what fraction of the board in 1 minute.

If Bart and Nelson started at the same time - what fraction of the board will remain covered after 1 minute?

Please show us what you have tried and exactly where you are stuck.

Please follow the rules of posting in this forum, as enunciated at:


Please share your work/thoughts about this problem.
 
This problem reminds me of a former professor that I had, Dr Arundhati Raychaudhuri. She would have her eraser in her left hand erasing as she was writing with her right hand. Her erasing speed was at least as great as her writing speed. She was a special teacher whom I have fond memories of. She was the person who taught me how to count.
 
Completely off subject. But I am surprised that any school still uses chalkboards. We(the university) replaced them with white-marker boards twenty-five or more years ago. The powers-that-be found that "white-boards" severed multiple functions. To write on them, use as a screen for over-heads, for projectors and computers all at half the cost.
 
pka said:
Completely off subject. But I am surprised that any school still uses chalkboards. We(the university) replaced them with white-marker boards twenty-five or more years ago. The powers-that-be found that "white-boards" severed multiple functions. To write on them, use as a screen for over-heads, for projectors and computers all at half the cost.
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This is true. Frankly, though, I like the idea of being the first instructor in a room after it's been cleaned because it's a fantastic rush to be the first one to mess up the board. 8) You can't get that with white boards.

-Dan
 
When I was the division chair we adopted a policy that anyone must clean the board at the end of each class, regardless of who did the writing. I got a lot of push-back from so-called senior faculty. My come-back was always "I do fill-out your evaluations".
 
I used to leave some nasty looking equation that had nothing to do with the class.

-Dan
 
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