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You walk one mile to school every day. You leave home at the same time each day, walk at a steady speed of 3 miles per hour, and arrive just as school begins. Today you were distracted by the pleasant weather and walked the first half mile at a speed of only 2 miles per hour. At how many miles per hour must you run the last half mile in order to arrive just as school begins today?

 May 13, 2020
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If you walk  at  3 mph   then  the normal time to  make it to school  is

 

(distance)  / (rate)  =    1 mi  / (3mi / h)  =  (1/3) hr  =  20 min

 

If you  walked  the first  half mile at 2 mph   the  time it took you  is

 

(1/2)mi  /( 2 mi / h)  =  (1/4) hr  =  15 min

 

Then....you must walk the last  1/2 mile  in 5 min  =  1/12  hr

 

So....to find the rate that you must run we have

 

distance / time  = rate

 

(1/2) mi  / (1/12) hr  = (12/2) mi / hr   =   6 mi / hr   =  6mph

 

cool cool cool

 May 13, 2020

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