Question

I usually take 72 minutes to reach college. On one fateful day, after traveling ${\frac{1}{3}}^{rd}$ of the distance, I realized that I left my ID card at home and returned to pick it up and then went back to college. To reach on time, I increased my speed by 30 kmph from the point I turned back home till the time I reached college. Assuming that no time was lost at home, what is my usual speed?

• A. 20 kmph
• B. 30 kmph
• C. 10 kmph
• D. 15 kmph

Answer 1

The correct option is B

30 kmph

Go from answer options .
Take a middle answer option.
Normal speed = 30kmph
Then distance between college and home = 30 $\times \frac{72}{60}$=36 km
Also, since time =72 minutes, Speed = 30 kmph.
Distance travelled before leaving back $=\frac{1}{3}$ of 36 =12 km and 24 minutes.
Therefore, time wasted = 24 minutes. Time left to reach = 72 - 24 =48 minutes.
New Speed = 30+30=60 kmph
Distance ot be traveled = 48 km
Time taken $=\frac{48}{60}\times 60$=48 minutes. Hence answer = option b.