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## Homework Statement

## Homework Equations

none

## The Attempt at a Solution

Is this correct?

Thanks.

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- Thread starter Evangeline101
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In summary, after solving for the jet's speed from Tokyo to Bangkok and correcting some algebra mistakes, it was determined that the jet's speed from Bangkok to Tokyo is 600 km/h.

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none

Is this correct?

Thanks.

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- #2

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The answer is correct.Evangeline101 said:## Homework Statement

[ ATTACH=full]101053[/ATTACH]

## Homework Equations

none

## The Attempt at a Solution

[ ATTACH=full]101054[/ATTACH]

Is this correct?

Thanks.

There are errors in your work starting with the table.

If x is the speed from Tokyo to Bangkok then reducing that by 200 gives a speed of x - 200 from Bangkok to Tokyo. Etc.

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Evangeline101 said:## Homework Statement

View attachment 101053

## Homework Equations

none

## The Attempt at a Solution

View attachment 101054

Is this correct?

Thanks.

Plug it in and see if it works.

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SammyS said:The answer is correct.

There are errors in your work starting with the table.

If x is the speed from Tokyo to Bangkok then reducing that by 200 gives a speed of x - 200 from Bangkok to Tokyo. Etc.

I understand where I made the error, the return trip speed decreased by 200 km/h, so it should have been (x-200) not (x+200), so I have corrected my answer:

Thanks for the help! :)

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There's still a problem, x is the Tokyo to Bangkok speed. That can't be 600mph. 600 - 200 is 400, and that doesn't work out.Evangeline101 said:I understand where I made the error, the return trip speed decreased by 200 km/h, so it should have been (x-200) not (x+200), so I have corrected my answer:

[ ATTACH=full]101104[/ATTACH]

Thanks for the help! :)

So, where is the problem?

You made a couple of errors.

Sign errors in going from

##-960000=2x^2-400x ##

to##2x^2+400x-960000= 0 ##

It should be ##2x^2-400x+960000= 0 ##

But there is no real solution to that.The problem is that it's the Tokyo to Bangkok time that's smaller, because the speed is greater. When you subtract to get 2 hours, you need to subtract in the opposite order.

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SammyS said:There's still a problem, x is the Tokyo to Bangkok speed. That can't be 600mph. 600 - 200 is 400, and that doesn't work out.

So, where is the problem?

You made a couple of errors.

Sign errors in going from

−960000=2x2−400x−960000=2x2−400x-960000=2x^2-400x to

2x2+400x−960000=02x2+400x−960000=02x^2+400x-960000= 0 It should be

2x2−400x+960000=02x2−400x+960000=02x^2-400x+960000= 0 But there is no real solution to that.

I tried doing it this way, but as you said there is no real solution.

SammyS said:The problem is that it's the Tokyo to Bangkok time that's smaller, because the speed is greater. When you subtract to get 2 hours, you need to subtract in the opposite order.

I don't understand what you mean, can you please explain?

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If x > 200, thenEvangeline101 said:I tried doing it this way, but as you said there is no real solution.

I don't understand what you mean, can you please explain?

##\displaystyle \frac{4800}{x-200}>\frac{4800}{x}##

.So you had these reversed.

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SammyS said:If x > 200, then

4800x−200>4800x4800x−200>4800x\displaystyle \frac{4800}{x-200}>\frac{4800}{x}.

So you had these reversed.

So even if I switch these two, can I not get the same answer I had originally? How does switching the two help with the answer to the problem? or is it just the proper way to write it?

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It's what is needed of you want to make everything consistent.Evangeline101 said:So even if I switch these two, can I not get the same answer I had originally? How does switching the two help with the answer to the problem? or is it just the proper way to write it?

As I stated in my first reply, the answer you gave for the time from Bangkok to Tokyo was correct. (600 km/hr)

But you had a number of inconsistencies.

Added in

You should get x = 800. Then x- 200 = 600, the answer.

Last edited:

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SammyS said:It's what is needed of you want to make everything consistent.

As I stated in my first reply, the answer you gave for the time from Bangkok to Tokyo was correct. (600 km/hr)

But you had a number of inconsistencies.

Added inEdit:

You should get x = 800. Then x- 200 = 600, the answer.

So like this:

- #11

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No.Not like that.Evangeline101 said:

The first three lines are correct.

After that, there are at least two Algebra mistakes.

As I stated in my previous post:

SammyS said:You should get x = 800. Then x- 200 = 600, the answer.

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This is an example from my lesson that I have been using as a reference to solve my problem:

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Right. And they did not make algebra mistakes. You did.Evangeline101 said:This is an example from my lesson that I have been using as a reference to solve my problem:

View attachment 101173

View attachment 101174

So (carefully) redo your algebra, starting at the third line of the following (from post #10), which is the last line that's correct.

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SammyS said:No.Not like that.

The first three lines are correct.

After that, there are at least two Algebra mistakes.

4800x - 4800x + 960 000 = 2x

960 000 = 2x

2x

x

(x+600) (x-800)

x= -600 or x = 800

Does this make more sense? did I fix the algebra errors? if not please show me where I made errors.

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Yes. That looks to be correct.Evangeline101 said:View attachment 101177

4800x - 4800x + 960 000 = 2x^{2}- 400x (960 000 is positive because I multiplied -4800 and -200)

960 000 = 2x^{2}- 400x (Now I move 960 000 to the right side and it becomes -960 000)

2x^{2}- 400x - 960 000 = 0

x^{2}- 200x - 480 000 = 0

(x+600) (x-800)= 0

x= -600 or x = 800

Does this make more sense? did I fix the algebra errors? if not please show me where I made errors.

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SammyS said:You should get x = 800. Then x- 200 = 600, the answer.

So since x = 800, we need to solve for the jets's speed from Bangkok to Tokyo, so (like you said) sub x = 800 into x- 200, which gives:

800 - 200 = 600 km/h

So the jet's speed from Bangkok to Tokyo is 600 km/h.

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Thanks for the help, I really appreciate it :)

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