Multiple choice

Alok travels a certain distance at a speed of 60 km/hr. If Prakash travels one fourth of that distance at a speed of 40 km/hr then at what speed he should travel the remaining distance if total time taken by both Alok and Prakash was same for the given journey? आलोक एक निश्चित दूरी की 60 किमी प्रति घंटा की दर से यात्रा करता है । यदि प्रकाश उस दूरी के एक चौथाई भाग की यात्रा 40 किमी/घंटे की दर से तय करता है, तो ज्ञात कीजिये कि उसे शेष दूरी को किस गति से तय करना चाहिए जिससे यात्रा में दोनों को लगने वाला समय समान हो ?

  1. 48 km/hr./(किमी./घंटा)

  2. 72 km/ hr./(किमी./घंटा)

  3. 75 km/hr./(किमी./घंटा)

  4. 96 km/hr./(किमी./घंटा)

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Alok's time = D/60. Prakash's time = (D/4)/40 + (3D/4)/v = D/160 + 3D/(4v). Setting equal: D/60 = D/160 + 3D/(4v). Solving gives v = 72 km/hr. This is a weighted average problem where the time for the slower first portion must be compensated by a faster second portion.