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avatar+262 

Antti entered a 10-kilometer race. His goal is to finish in one hour. He starts off sprinting, and completes the first 2 kilometers of the race at an average speed of 12 kilometers per hour.

To achieve his goal of a one-hour finish time, what average speed must Antti maintain for the last 8 kilometers of the race?

Enter your answer as a number in decimal form, without units.

 Mar 11, 2021
 #1
avatar+31281 
+3

For AVERAGE SPEED calculations , you have to consider TIME

   because    km run / TIME = average 'speed'

 

He needs to average   6 km / hour   (his goal)   

   he has run 2 km  @ 12 km/ hr       2km / 12 km/hr = 1 / 6  hr   (10 minutes)

          he has to run the remaining   8 km   in 50 minutes   (5/6 hr)       8 km/ (5/6 hr ) =  48/5  km/ hr     =  9.6   km / hr

 

 

EGAD....I had Anti running a 6k race     edited 

 Mar 11, 2021
edited by ElectricPavlov  Mar 11, 2021
edited by ElectricPavlov  Mar 11, 2021
 #4
avatar+31281 
+2

He needs to average   10 km / hour   (his goal)   

   he has run 2 km  @ 12 km/ hr       2km / 12 km/hr = 1 / 6  hr   (10 minutes)

          he has to run the remaining   8 km   in 50 minutes   (5/6 hr)       8 km/ (5/6 hr ) =  48/5  km/ hr     =  9.6   km / hr

ElectricPavlov  Mar 11, 2021
 #2
avatar+118069 
+3

At  12K per hour....it takes him  5 min per each kilometer  (do you see this  ???  )

 

(Think about it.....there are 12 equal parts  in one hour  ...so...he runs 2 km in 10 min )

 

So....he   has to cover   10  - 2    =  8  kilometers in 50 remaining  minutes =  5/6 hr

 

So

 

Rate    = Distance /  Time

 

Rate  =  8  /( 5/6)   =    8  * (6/5)   =  48/5 km /hr    =  9.6 km/ hr    for the rest of the race

 

 

cool cool cool

 Mar 11, 2021
edited by CPhill  Mar 11, 2021
 #3
avatar+262 
0

I am confused what the answer should be and i typed 4.8 and it was wrong.

 Mar 11, 2021

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