Maths problem

[Lala81]

  On 10/15/2018 at 10:51 AM, Angcheek said:

ai yo ...... made until so complicated .  

 

If you draw out the graph  2^x + x^2  ,   x^2 will give  2 answ . 2^x  will give a exponential effect to the result  

 

while x= 6 is a more absolute answ , x = -9.999995 is not exactly "real" as it will never hit 10.  just that  with x -> - infinity, 

the  2^x became extremely small or negligible 

 

    primary school theory 

 

u math teacher issit? 

[Angcheek]

  On 10/15/2018 at 11:20 AM, Lala81 said:

u math teacher issit?

No

[1fast1]

  On 10/15/2018 at 10:51 AM, Angcheek said:

ai yo ...... made until so complicated .

 

If you draw out the graph 2^x + x^2 , x^2 will give 2 answ . 2^x will give a exponential effect to the result

 

while x= 6 is a more absolute answ , x = -9.999995 is not exactly "real" as it will never hit 10. just that with x -> - infinity,

the 2^x became extremely small or negligible

 

primary school theory

Haha yes 2^x goes to 0 as x goes to -infinity. But the x^2 how?

 

It's a balance between the two terms lah.

 

Now better chill before I start laying on some Intermediate Value Theorem in this thread.

 

I make things exactly as complicated as they need to be for rigour. No more, no less.

[DACH]

  On 10/15/2018 at 12:15 PM, Turboflat4 said:

Haha yes 2^x goes to 0 as x goes to -infinity. But the x^2 how?

 

It's a balance between the two terms lah.

 

Now better chill before I start laying on some Intermediate Value Theorem in this thread.

 

I make things exactly as complicated as they need to be for rigour. No more, no less.

 

You are a lecturer, or engineer?

 

[Atrecord]

  On 10/15/2018 at 4:40 AM, Ender said:

This one chinese or math question?   

I think it's 130cm..

 

you're right leh.

 

I couldn't figure it out myself, and needed to ask my friends leh... jialat... can't visualise it initially

[1fast1]

  On 10/15/2018 at 10:38 AM, Lala81 said:

I didn't burn my notes after A levels but i might as well have set fire to all these knowledge.

I was a poor mathematics student at best. Just getting by with repeated ten year series in O levels and never really understood the higher concepts. Similar to my physics which i struggled at JC level.

 

Haha ok, i'll watch some online videos on what u mentioned earlier and try to refresh some brain cells

I never really had to work hard at Math or Physics. That's why I loved those subjects because I'm fundamentally damn lazy. I read ahead because I found the material at the current level too easy and was hungry for more (so there was definite interest). Didn't struggle, skipped a lot of lectures at JC level (teachers didn't really care with my results), just submitted the homework regularly. Did the S papers and the Physics Olympiad. Basically, these two subjects came intuitively to me.

 

Not like Chemistry (hated it) and Biology (I wanted it wiped off the face of the earth). Ironic that I ended up becoming a doctor like you. Filial son etc.

 

I should've accepted the PSC OMS to Caltech. Would've been happier. Maybe. Oh well.

[Atrecord]

  On 10/15/2018 at 9:47 AM, Angcheek said:

hahah my friend also posted this to me ...... took me awhile to figure out the answ . 

 

Must use primary school reasoning 

 

answ C 

 

So you actually managed to figure it out yourself, after a while?

 

Then you better than me

 

i tot for a while, couldn't get it and proceeded to ask my friend for answer - and explanation...

[1fast1]

  On 10/15/2018 at 3:55 PM, DACH said:

You are a lecturer, or engineer?

 

Doctor like @lala81.

  On 10/15/2018 at 1:43 AM, Atrecord said:

Wah the maths problems all very cheem...

 

Came across this:

 

Cat n table.jpeg

Assume they're asking for height of table?

 

h - table ht

s - short cat (sitting)

t - tall cat (standing)

 

h+t-s = 150

h+s-t = 110

 

Add, cancel, divide by two.

[Atrecord]

  On 10/15/2018 at 4:23 PM, Turboflat4 said:

Doctor like @lala81.

Assume they're asking for height of table?

 

h - table ht

s - short cat (sitting)

t - tall cat (standing)

 

h+t-s = 150

h+s-t = 110

 

Add, cancel, divide by two.

 

Looking through your cheem cheem solutions for the other sophisticated problem, as well the simple solution to this simple-looking-yet-tricky problem, i can only say i'm si bey impressed...

 

I couldn't get the answer, and even when my friend explained, it took me a while to understand it...

[1fast1]

  On 10/15/2018 at 4:29 PM, Atrecord said:

Looking through your cheem cheem solutions for the other sophisticated problem, as well the simple solution to this simple-looking-yet-tricky problem, i can only say i'm si bey impressed...

 

I couldn't get the answer, and even when my friend explained, it took me a while to understand it...

Bro, simple or chim doesn't matter. As the Chinese saying goes, black cat or white cat doesn't matter; as long as it catches mice, it's a good cat.

 

Nice that I remembered that in the context of this cat question.

 

But to illustrate, let me pose a question of my own. There is a nice anecdote attached to this one, which I'll reveal later.

 

Anyway, the question is:

 

  Quote

Two trains are 20 miles apart on the same track heading towards each other at 10 miles per hour, on a collision course. At the same time, a bee takes off from the nose of one train at 20 miles per hour, towards the other train. As soon as the bee reaches the other train, it instantaneously reverses direction and heads off at 20 miles per hour back towards the first train. It continues to do this until the trains collide, killing the bee.

 

The question is: how far (distance) does the bee fly before it gets squished?

Edited October 15, 2018 by Turboflat4

[Ender]

  On 10/15/2018 at 4:44 PM, Turboflat4 said:

Two trains are 20 miles apart on the same track heading towards each other at 10 miles per hour, on a collision course. At the same time, a bee takes off from the nose of one train at 20 miles per hour, towards the other train. As soon as the bee reaches the other train, it instantaneously reverses direction and heads off at 20 miles per hour back towards the first train. It continues to do this until the trains collide, killing the bee.

 

The question is: how far (distance) does the bee fly before it gets squished?

I think the bee would have travel 20 miles before kenna squashed.

 

Becouse the trains collide in 1 hour.  So that's the time the bee has to traveled back and forth at 20 mile/hr. 

[1fast1]

  On 10/15/2018 at 6:45 PM, Ender said:

I think the bee would have travel 20 miles before kenna squashed.

 

Becouse the trains collide in 1 hour.  So that's the time the bee has to traveled back and forth at 20 mile/hr. 

 

Excellent, Ender. Correct answer. Simple, yes?

 

Now, can you think of what the "chim" method might be? Remember there's a "moral" to this story I'll share later.

[mersaylee]

  On 10/15/2018 at 4:29 PM, Atrecord said:

Looking through your cheem cheem solutions for the other sophisticated problem, as well the simple solution to this simple-looking-yet-tricky problem, i can only say i'm si bey impressed...

 

I couldn't get the answer, and even when my friend explained, it took me a while to understand it...

I never bother to attempt...as I know I can find the answer here one.

 

Lazy or smart? I don’t mind if it’s both.

[Atrecord]

  On 10/15/2018 at 4:44 PM, Turboflat4 said:

Bro, simple or chim doesn't matter. As the Chinese saying goes, black cat or white cat doesn't matter; as long as it catches mice, it's a good cat.

 

Nice that I remembered that in the context of this cat question.

 

But to illustrate, let me pose a question of my own. There is a nice anecdote attached to this one, which I'll reveal later.

 

Anyway, the question is:

 

 

wah... becos of this, i couldn't sleep last night, as i took a quick glance before i logged off

 

joke only.

 

I didn't catch the logic like @ender did, but looking at the pattern of the to-and-fro bee flight, i was wondering whether it will add up to one full 'circle' of the distance between the 2 trains before moving off. But no explanation, as the workings would go till infinite.

 

you guys are

[Ender]

  On 10/15/2018 at 11:50 PM, Turboflat4 said:

Excellent, Ender. Correct answer. Simple, yes?

 

Now, can you think of what the "chim" method might be? Remember there's a "moral" to this story I'll share later.

Before I began coaching my son for his psle, I would had brute force with this method,

1. Find distance the bee traveled from train A to B.

2. With remainder distance between the trains, find the distance the bee would traveled from B to A

3. Repeat 1 and 2 til the bee traveled distance is 0

4. Add up all the distances found above.

 

The primary school syllabus taught me to look at problems simply like a kid. Of course this would not work for problems from the RI's math club.

[Ben5266]

i use binary to calculate. Or the method we use to calculate the subnet mask.

 

2(0) ! 2(1) ! 2(2) ! 2(3) ! 2(4) ! 2(5) ! 2(6) ! 2(7) 

1     ! 2      ! 4     ! 8      ! 16   ! 32    ! 64   ! 128 

 

So, 7 is out.

 

6 x 6 = 36.

 

Bingo!

 

Brute force?

 

So, if the subnet mask is 255 = 11111111

If the subnet mask is 254 = 11111110

subnet mask is 252 = 11111100

 

I guess this is the introduction to the binary calculation.

[1fast1]

  On 10/16/2018 at 1:23 AM, Ender said:

Before I began coaching my son for his psle, I would had brute force with this method,

1. Find distance the bee traveled from train A to B.

2. With remainder distance between the trains, find the distance the bee would traveled from B to A

3. Repeat 1 and 2 til the bee traveled distance is 0

4. Add up all the distances found above.

 

The primary school syllabus taught me to look at problems simply like a kid. Of course this would not work for problems from the RI's math club.

 

That's basically it, but you do realise that if you did that literally, you would be calculating forever?

 

Because what you've got at step 3 is an infinite loop. The distance never quite goes to zero.

 

What you'll end up with is an infinite geometric series with a finite sum (that's what you need to find).

 

It's rather tedious to do this. This is the "chim" method.

 

The cute anecdote (apparently true, although the exact details vary in the telling) is that the great genius (founder of game theory among other things) and almost literal human calculator John von Neumann was posed this question. He answered almost immediately (less than two seconds) without needing to write anything down.

 

The questioner then said "Oh, so you know the easy method to do this problem then? Most mathematicians immediately try to sum the infinite series."

 

To which von Neumann is said to have replied either:

 

"I *did* sum the series."

 

"There's another method?"

 

"What could be easier than summing the series?"

 

etc. etc. (depends on the exact telling, as I mentioned).

 

The "moral" of the story is that if you're as brilliant as von Neumann, "clever" shortcuts are unnecessary and "chim" is no different than "simple".

[Sosaria]

  On 10/15/2018 at 4:17 PM, Turboflat4 said:

I never really had to work hard at Math or Physics. That's why I loved those subjects because I'm fundamentally damn lazy. I read ahead because I found the material at the current level too easy and was hungry for more (so there was definite interest). Didn't struggle, skipped a lot of lectures at JC level (teachers didn't really care with my results), just submitted the homework regularly. Did the S papers and the Physics Olympiad. Basically, these two subjects came intuitively to me.

 

Not like Chemistry (hated it) and Biology (I wanted it wiped off the face of the earth). Ironic that I ended up becoming a doctor like you. Filial son etc.

 

I should've accepted the PSC OMS to Caltech. Would've been happier. Maybe. Oh well.

 

Why you no take Further Math? Instead of Bio. That would've made JC even more relaxing for you. I did that, but of course, the doors to med course is well and truly closed once take that option, no matter how good the results.

Edited October 16, 2018 by Sosaria