A person covers a distance in 21 minutes. If runs at a speed of 12 km per hour on an average. Find the speed at which he must run to reduce the time of journey to 5 minutes.  Choose the correct choice
A) 18 m/s
B) 4 m/s
C) 14 m/s
D) 10 m/s
E) 5 m/s
Explanation:   T = 21 m   Spees = 12 kmph   = 12 x 5/18 = 10/3 m/s   Let new speed be "x"   21 x (10/3) = 5x   x = 14 m/s   Answer: Option 14 m/s
<result>C</result>
A person covers a distance in 21 minutes. If runs at a speed of 12 km per hour on an average. Find the speed at which he must run to reduce the time of journey to 5 minutes.