Question

A boat travels a total distance of 25 km in 0.75 hours. The driver of the boat turns around and travels the same 25 km in 0.5 hours. What is the average speed of the boat for the entire trip?

67 km/hr

20 km/hr

0.025 km/hr

40 km/hr

Answer 1

Step 1 : distance travelled = 25 km , time taken = 0.75 hour

=> Distance = speed × time

= > speed = distance / time = 25 km / 0.75 hour = 33.33 km/hr

= > x = 33.33 km/hr

Step 2: y = speed of second part = distance / time = 25 km /0.5 hour = 50 km/hr

=>y = 50 km/hr

When distance is same , we use the formula

=> V_avg = {(2xy) / (x+y)} ......................(1)

& When time is same for both part

=>V_avg = (x + y) / 2 .........................(2)

Substituting the value obtained in equation(1). => V_avg = (2 × 33.33 × 50)/(33.33 + 50) = 3333 / 83.33 = 39.99 km/hr = 40 km/hr

Option (d) is correct.