+0  
 
0
66
1
avatar

Jeff and Kirk can build a​ 75-ft retaining wall together in 6 hours. Because Jeff has more​ experience, he could build the wall by himself 2 hours quicker than Kirk. How long would it take Kirk​ (to the nearest​ minute) to build the wall by​ himself?

 Jan 28, 2020
 #1
avatar+21763 
+2

1 wall/ (1 wall/ j+ 1 wall/ k)   = 6     where  j  and  k are the times for each  Jeff and Kirk

 

1 wall/ (j)   =   1 wall/(k  -2)    sub this into the first equation above

 

1 /  (( 1/(k  -2) + 1/k  )  = 6

1  /   k-2 +k  / (k^2 - 2k)

 

(k^2-2k) / (2k-2)   = 6

k^2 -2k = 12k - 12

k^2 -14k + 12 = 0      k =  13.0828   or   .91724  hrs (throw out)

k=13.0828 hrs   then   j  = 11.0828 hrs

 

check     1 /   (1/11.0828  + 1/13.0828)      = 6 ?

                        6                                         = 6        Check !

 

 

Kirk by himself =    13.0828 hrs   =  ~~13 hrs 5 mins

 Jan 28, 2020

55 Online Users

avatar