How long did she spend runnung?

Question

Mary competed in a biathalon that involved running and cycling. She covered a total distance of 65 miles in 3 hours. If she ran at a rate of 5 mph and cycled at a rate of 25 mph, how long did she spend running?

Answer 1

d=r*t

65=5*t+25(3-t)

65=5t+75-25t

65=75-20t

20t=75-65

20t=10

t=10/20

t=1/2 hour running

Answer 2

d = r · t

 

For running

d = 5(3 - t)

 

For cycling

d = 25t

 

The two distances add to 65

5(3 - t) + 25t = 65

15 - 5t + 25t = 65

15 + 20t = 65

20t = 50

t = 2.5

 

She spent one-half hour running.

 

Check

(0.5)5 + (2.5)(25)

2.5 + 62.5

65