There is a road beside a river.Two friends started from a place A, moved to a temple situated at another place B and then returned to A again. One of them moves on a cycle at a speed of 12 km/hr, while the other sails on a boat at a speed of 10 km/hr. If the river flows at the speed of 4 km/hr, which of the two friends will return to place A first ?
A. 5.4 km /hr
B. 7.2 km /hr
C. 8.4 km/hr
D. 9.6 km /hr

• ans :
  speed of cycle both side on road will be same
  average speed of cycle = 12 kmhr
  downstream , boat speed =10+4= 14kmhr
  upstream = 10- 4 = 6kmhr
  
  averge of boat speeds =( 2* 14* 6)/14+6=8.4 kmhr
  
  therefore , friend on cycle will return to place A first.
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