P and Q take part in 400 m race. P runs at 12 km/hr. P gives Q a start of 20 m and still beats him by 13 seconds. The speed of Q is:
(Round up to two decimal places.)
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 10.29 km/hr.
P's speed = 12 km/hr = 12 × (5/18) m/s = 10/3 m/s
Time taken by P to finish the race = Distance/Speed = 400/(10/3) = 120 seconds
Q gets a start of 20 m, so he runs 400 - 20 = 380 m
P beats Q by 13 seconds.
Time taken by Q to finish the race = 120 + 13 = 133 seconds
Q's speed = (380/133) m/s = (380/133) × (18/5) km/h = 10.285... km/h = 10.29 km/h (approx)
Therefore, the speed of Q is 10.39 km/hr.