Jeff takes 20 minutes to jog around the race course one time, and 25 minutes to jog around a second time. What is his average speed in miles per hour for the whole jog if the course is 3 miles long?

A. 6
B. 8
C. 10
D. 12
E. 14
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various methods to do it--

I)
speed first time =\(\frac{3}{20}*60 = 9 mph\)..
speed second time = \(\frac{3}{25}*60 = 7.2mph\)..

so average speed has to be between 7.2 and 9..
ONLY 8 is given
ans B..

II) the two speed are 9mph and 7.2 mph..
so average speed by formula when distance covered is same on both occasions = \(\frac{2ab}{(a+b)} = \frac{2*9*7.2}{(9+7.2)}= \frac{2*7.2*9}{9(1+0.8)} = \frac{2*7.2}{1.8} = 2*4 = 8\)..
ans B

III)
distance = 3+3 = 6 miles
time taken = 20+25 = 45 min = \frac{45}{60} hour = \frac{3}{4} hour
avg speed = \(6/\frac{3}{4}= 8\)
B
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Avg Speed= total distance /total time

3+3/20+25
6/45

Since we have to find the speed in miles/hr, multiply the above number by 60

6*60/45= 8 miles/hr

B is the answer
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The average speed is:

6/(20/60 + 25/60) = 6/(45/60) = 360/45 = 8 mi/hr

Answer: B
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