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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:
Answer & Solution
Correct Answer:
Option
B
Total distance travelled :
= (10 + 12) km
= 22 km
Total time taken :
$$\eqalign{ & = \left( {\frac{{10}}{{12}} + \frac{{12}}{{10}}} \right){\text{ hrs}} \cr & = \frac{{61}}{{30}}{\text{ hrs}} \cr} $$
∴ Average speed :
$$\eqalign{ & = \left( {22 \times \frac{{30}}{{61}}} \right){\text{ km/hr}} \cr & = 10.8{\text{ km/hr}} \cr} $$
= (10 + 12) km
= 22 km
Total time taken :
$$\eqalign{ & = \left( {\frac{{10}}{{12}} + \frac{{12}}{{10}}} \right){\text{ hrs}} \cr & = \frac{{61}}{{30}}{\text{ hrs}} \cr} $$
∴ Average speed :
$$\eqalign{ & = \left( {22 \times \frac{{30}}{{61}}} \right){\text{ km/hr}} \cr & = 10.8{\text{ km/hr}} \cr} $$
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