Question

A man is travelling by car at the rate of 40 km/hr. After every 80 km, he rests for 20 min. How long will he take to cover a distance of 240 km?
(a) 6 hr 40 min
(b) 6 hr
(c) 6 hr 20 min
(d) 7 hr

Answer 1

Hint: We will first calculate the total time for which he has taken rest in a span of 240 km. And then we will apply the formula \[\text{time}=\dfrac{\text{distance}}{\text{speed}}\] to find the time if rest was not taken. Finally we will get the answer by adding both these times.

Complete step-by-step answer:
Speed of the car mentioned in the question is 40 km/hr.
It is mentioned in the question that after every 80 km he takes rest for 20 min. So in travelling a total distance of 240 km he takes rest once after 80 km and then again after 160 km. So he will take rest for a total of 20 plus 20 minutes.
So using these information we get,
Total rest time \[=20+20=40\,\min ......(1)\]
Speed\[=40\,km/hr......(2)\]
And total distance \[=240\,km......(3)\]
Now we know that time is distance divided by speed. Hence using this information we get,
\[\Rightarrow \text{time}=\dfrac{\text{distance}}{\text{speed}}.......(4)\]
So substituting value of distance from equation (3) and value of speed from equation (2) in equation (4) we get,
\[\Rightarrow \text{time}=\dfrac{240}{40}=6\,hr.......(5)\]
So the total time taken to cover 240 km is 6 hr plus time given in rest that is 40 min.
Hence from equation (1) and equation (5) we get the total time taken as 6 hr 40 min.
Thus, the correct answer is option (a).

Note: Here we need to remember the relation between speed, time and distance. Also in a hurry we may forget to add the time taken for rest and hence we need to be careful while doing this. Also we should not forget to mention the units else marks will be deducted.