Subject: mathqa
Question: a boy rides his bicycle 10 km at an average speed of 12 km / hr and again travels 12 km at an average speed of 10 km / hr . his average speed for the entire trip is approximately ?
Option: 
A: 10.7 km / hr
B: 10.8 km / hr
C: 17.8 km / hr
D: 30.8 km / hr
Answer: B