Aptitude Discussion

Q. |
The speed of a bus during the second hour of its journey is twice that in the first hour. Also, its speed during the third hour is two-third the sum of its speeds in the first two hours. Had the bus travelled for three hours at the speed of the first hour, it would have travelled 120 km less. Find the average speed of the bus for the first three hours. |

✖ A. |
60 kmph |

✖ B. |
70 kmph |

✖ C. |
80 kmph |

✔ D. |
100 kmph |

**Solution:**

Option(**D**) is correct

Let the speed for the first hour be '$s$' kmph.

Speed during second hour = $2s$ kmph.

And speed in the third hour

= \(\dfrac{2}{3}\times 3s=2s\) kmph

Distance travelled = $5s$ km

Had it travelled at s kmph, distance travelled would have been equal to 3s kmph.

Given, $5s−3s=120$

$⇒ s=60$

Average speed for the first three hours:

\(=\dfrac{5s}{3}\)

= **100 kmph**