Join 60,000+ competitive exam aspirants
or with email
Your Cart
Subtotal₹0
Total₹0
Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
Join 60,000+ competitive exam aspirants
Shalini travels a distance of 270 km with speed of 54 km/h and 300 km with 30 km/h by her car. Find the average speed (in km/h) of Shalini.
47
38
43
44
38
Calculate the two individual times first: 270/54=5 hours and 300/30=10 hours. Then, Average Speed = (270+300)/(5+10)=570/15=38 km/h.
Distance d1 = 270 km, Speed s1 = 54 km/h; Distance d2 = 300 km, Speed s2 = 30 km/h.
Average Speed=TotalTimeTotalDistance=s1d1+s2d2d1+d2
Calculate the two individual times first: 270/54=5 hours and 300/30=10 hours. Then, Average Speed = (270+300)/(5+10)=570/15=38 km/h.
Students often mistakenly take the simple average of the speeds, i.e., (54+30)/2=42 km/h, which is incorrect.
Calculate time for the first journey
Using the formula Time=Distance/Speed, time taken for the first part is t1=270/54.
t1=5 hours
Calculate time for the second journey
Similarly, time taken for the second part is t2=300/30.
t2=10 hours
Calculate Average Speed
Total distance is 270+300=570 km, and total time is 5+10=15 hours. Now apply the average speed formula.
Average Speed=15570=38 km/h
B is correct because the total distance of 570 km divided by the total time of 15 hours results in 38 km/h.
This concept is foundational for 'Boats and Streams' and 'Trains' problems, where calculating total time taken is always the safest approach.
Get instant step-by-step AI explanations, full shift Previous Year Papers (SSC GD, RRB, SSC JE), and regional rank analysis on the official Examoogle App.
Free Download • 100K+ Aspirants