question_answer

Two cars A and B starts at the same time from two points P and Q, respectively- A starts from P to Q, while B starts from Q to P. They arrive their destination in \[3\frac{1}{5}\] h and \[7\frac{1}{2}\] h, respectively. At what speed does car A travels, if car B travels with a speed of 36 km/h?

A)  24 km/h

B)  54 km/h

C)  81 km/h

D)  72 km/h

Correct Answer: C

Solution :

Speed of B = 36 km/h Time taken \[=7\frac{1}{5}\text{h}\,\text{=}\,\frac{36}{5}\,\text{h}\] Distance = Speed \[\times \] Time \[\left( 36\times \frac{36}{5} \right)\,\text{km}\] \[=\frac{1296}{5}\,km\] Distance between P and \[Q=\frac{1296}{5}\,km\] Time taken by \[A=3\frac{1}{5}\,\text{h}=\frac{16}{5}\text{h}\] Speed = Distance/Time \[=\frac{1296}{5}\times \frac{5}{16}=81\,\text{km/h}\]