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# 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 t

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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?

Mar 11, 2021

#1
+31281
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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

Mar 11, 2021
edited by ElectricPavlov  Mar 11, 2021
edited by ElectricPavlov  Mar 11, 2021
#4
+31281
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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
+118069
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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

Mar 11, 2021
edited by CPhill  Mar 11, 2021
#3
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I am confused what the answer should be and i typed 4.8 and it was wrong.

Mar 11, 2021