We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive pseudonymised information about your use of our website. cookie policy and privacy policy.
 
+0  
 
+1
121
8
avatar+1112 

Joe flew 300 miles with the wind in two hours. After flying against the wind for 2 hours, he had made 270 miles of the return trip. Find the wind speed and the speed of the plane in still air.

 

with -              r      *      t      =      d

 

against-

 

 

 

This is a motion problem but I don't know how to do it.

 May 7, 2019
 #1
avatar+19724 
+2

When flying WITH the wind his rate is   s +w        where s = plane speed  w = wind speed

 

so   d = r * t

       300 = (s+w) * 2

 

 

AGAINST the wind, his rate is   s - w

so  270 = (s-w)*2                                       Now you have two equations and two unknowns....solve the system of equations to find ' s '

 May 7, 2019
 #2
avatar+1112 
+2

I can't solve that, it has two variables.

SmartMathMan  May 7, 2019
edited by SmartMathMan  May 7, 2019
 #3
avatar+19724 
+2

What box?

ElectricPavlov  May 7, 2019
 #4
avatar+1112 
+2

it is supposed to be the box way of solving it, nevermind. But I can't solve a problem with two variables.

SmartMathMan  May 7, 2019
edited by SmartMathMan  May 7, 2019
 #5
avatar+1112 
+1

I got plane speed is  142.5 mph and wind speed is 7.5 mph.

 May 7, 2019
 #7
avatar+19724 
+1

Correct-a-mundo! cheeky

ElectricPavlov  May 7, 2019
 #6
avatar+19724 
+1

It is WAY easier to solve this NOT using the clumsy box method:

 

You have two equations:

300 = 2(s+w)     or    150 = s+w      (by dividing both sides of the equation by 2)

270 = 2 (s-w)     or    135 = s-w           <------ Now ADD the two equations together

                                 285 + 2s       thus s = 142.5 = plane speed in still air

 

 

 

I havn't any idea how to make this into a quadratic to solve by the Box method

(this ' box method', I think is crazy....sorry you are being taught this method)...

 May 7, 2019
 #8
avatar+1112 
+2

sorry, thx i got it!!!!!!!! we have to use the box method sadly.

SmartMathMan  May 7, 2019

30 Online Users

avatar
avatar
avatar