Multiple choice

The distance from the railway station to a village is four kilometres. A boy and a car left the station at the same time for village. Ten minutes later, the boy met the car on its way back from the village. After he had walked another 1/14 km, he met the car once again which drove to the station and was headed back for the village. Find the respective speeds (in km/hr) of the boy and the car, assuming them to be uniform with no stoppages.

  1. 4 km/hr, 50 km/hr

  2. 2.5 km/hr, 40 km/hr

  3. 3 km/hr, 45 km/hr

  4. 3 km/hr, 60 km/hr

  5. 4 km/hr, 45 km/hr

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

Let v_b be the boy's speed and v_c be the car's speed. The boy walks 4 km. The car travels to the village and back. Using relative speed and time equations for the two meetings, we solve the system of equations. For the first meeting at 10 minutes (1/6 hr), the boy walked 1/6 * v_b and the car traveled 4 + (4 - 1/6 * v_b). Solving these yields 3 km/hr and 45 km/hr.

AI explanation

The boy walks at a constant speed while the car makes continuous trips between the station and the village. In the first 10 minutes, the boy walks (10 multiplied by v_boy) divided by 60 km while the car travels to the 4 km village marker and returns, meaning their combined distance equals 8 km; this gives the equation (v_boy plus v_car) multiplied by (1 divided by 6) equals 8, so v_boy plus v_car equals 48. The boy then walks an additional 1/14 km, taking (1 divided by 14) divided by v_boy hours, during which the car returns to the station and comes back to meet him; the car's total travel distance of 4 km plus its position relative to the station equals its speed multiplied by that time. Testing the option where the boy walks at 3 km/hr, the 1/14 km walk takes 1/42 hours, during which the car travels 45 multiplied by 1/42, totaling 15/14 km; since the car travels from the 4 km village marker back to the station and then out again for 1/14 km, its position perfectly matches the boy's 1/14 km distance from the station. Therefore, the respective speeds are 3 km/hr for the boy and 45 km/hr for the car.