What is the Number of Einstein's Students?

[chawki]

Homework Statement

Einshtein once was asked about the number of his students, he said: 1/5 of my students study maths, 1/7 study chemistry, 20 students doesn't study at all.

Homework Equations

How many students does he have?

The Attempt at a Solution

My guess was 20.
I hope my answer is at least close to the right answer, there are many ways on how to look to this problem..

 

[chronon]

Homework Statement

Einshtein once was asked about the number of his students, he said: 1/5 of my students study maths, 1/7 study chemistry, 20 students doesn't study at all.

If you assume that the options are exclusive and account for all of the students then you get fractional students. The original, from Page 193 of Mathematical fun, games and puzzles by Jack Frohlichstein is 1/2 study maths, 1/3 study geometry, 1/7 study chemistry, 20 don't study at all. and doesn't have this problem

 

[chawki]

ok, so what about the answer ?

 

[L2E]

Take X as the total number of students:

X*(1/2 + 1/3 + 1/7) + 20 = X

Then use your algebra.

 

[HallsofIvy]

Homework Statement

Einshtein once was asked about the number of his students, he said: 1/5 of my students study maths, 1/7 study chemistry, 20 students doesn't study at all.

Homework Equations

How many students does he have?

The Attempt at a Solution

My guess was 20.
I hope my answer is at least close to the right answer, there are many ways on how to look to this problem..

That's not even a good guess. If he has 20 students and 20 "don't study at all", he couldn't possibly have "1/4 study maths 1/7 study chemistry".

I suspect that you did not actually "guess". You heard the number 20 and echoed it. That reminds me of the girl who was asked on a quiz to name the country directly east of Germany- her answer, "Germany"!

 

[SammyS]

Perhaps the 1/7 who study chemistry also study math. That would give 25 students total.

If the 1/7 & 1/5 are exclusive, then there are at least 30 & 10/23 students.

 

[chawki]

That's not even a good guess. If he has 20 students and 20 "don't study at all", he couldn't possibly have "1/4 study maths 1/7 study chemistry".

I suspect that you did not actually "guess". You heard the number 20 and echoed it. That reminds me of the girl who was asked on a quiz to name the country directly east of Germany- her answer, "Germany"!

I don't like your attitude.
It was my guess, I had about 10 seconds left, and I thought ''he has at least 20, so i wrote 20 students'' Not much time to think about it or to do fraction calculations.

You can't just use the fact of being a mentor and suspect things on me.
Keep your words under control, You can't just come here and say that i heard things and i wrote them, and furthermore you make a joke about me when you mention that girl story or what ever you encountered during your career... who cares...If you don't know how to provide help or you don't know the solution, you better be quiet rather than assuming things on people you don't even know.

And one more thing, read the problem as i wrote it in post #1 ''Einshtein once was asked about the number of his students, he said: 1/5 of my studen ts study maths, 1/7 study chemistry, 20 students doesn't study at all''.

 

[SammyS]

I don't think H.o.I was trying to be mean spirited, although I can see how you read that post that way. I've read lots of his posts, and that would be very uncharacteristic of H.o.I.

 

[VietDao29]

I don't like your attitude.
It was my guess, I had about 10 seconds left, and I thought ''he has at least 20, so i wrote 20 students'' Not much time to think about it or to do fraction calculations.

You can't just use the fact of being a mentor and suspect things on me.
Keep your words under control, You can't just come here and say that i heard things and i wrote them, and furthermore you make a joke about me when you mention that girl story or what ever you encountered during your career... who cares...If you don't know how to provide help or you don't know the solution, you better be quiet rather than assuming things on people you don't even know.

And one more thing, read the problem as i wrote it in post #1 ''Einshtein once was asked about the number of his students, he said: 1/5 of my studen ts study maths, 1/7 study chemistry, 20 students doesn't study at all''.

You had like 10 seconds to think about that. Yes, but did you mention that in the first post? How are we supposed to know that you did have 10 seconds to make that guess?

And one more thing, didn't you think about that problem after the test? If you did, then it was not true that you only had 10 seconds to make that guess! There is plenty of time after the test, no?

Moreover, how can 7 ever divide 20? Is your guess even valid? How much time do you need to justify this guess?

Yes, I know that you may take HallsofIvy's post to be offensive. But doing Maths is not just about making guess(es). Making guess is only one stage of it. Other stages are justifying, and proving that guess.

 

[berkeman]

Thread closed by berkeman