\(\frac{2}{5}\)th of the journey is covered at a speed of 30 km/h, \(\frac{1}{4}\)th of the journey at a speed of 25 km/h and rest at 60 km/h. What is an avg. speed for the whole journey?
Answer & explanation
Correct answer: option 2
Let total distance = 20
\(\frac{2}{5}\)th \(\frac{1}{4}\)th Remaining
Distance ratio 8 : 5 : 7
Speed 30 : 25 : 60 (LCM of 30, 25, 60 = 300)
multiply distance ratio by 300 to easy calculation
D → 8 × 300 : 5 × 300 : 7 × 300
S → 30 : 25 : 60
Avg. speed = \(\frac{20 × 300}{80 + 60 + 35}\) = \(\frac{6000}{175}\) = 34.28