A man rides at the rate of 30km/hr. But stops 20minutes to change horses at the end of every 60th kilometer. How long will he take to go a distance of 180 kilometers?
Choose the correct choice from the following answers:
A) 5hr  B) 6hr 30min  C) 6hr 40min  D) 7hr 20min  E) 9hr
speed of man = 60km/hr   number of rests = (180/60)-1= 
<gadget id="calculator">(180/60)-1</gadget>
<output>2</output>
2   time taken for the man= (180/30)+2*(20/60) = 6 hr 40 min   Answer is 6hr 40min
<result>C</result>
A man rides at the rate of 30km/hr. But stops 20minutes to change horses at the end of every 60th kilometer. How long will he take to go a distance of 180 kilometers?