A and B go around a circular track of length 150 m on a cycle at speeds of 36 kmph and 54 kmph. After how much time will they meet for the first time at the starting point? Choose one:  A) 30 sec  B) 198 sec  C) 178 sec  D) 665 sec  E) 276 sec

Rationale: "time taken to meet for the first time at the starting point = lcm { length of the track / speed of a , length of the track / speed of b } = lcm { 150 / ( 36 * 5 / 18 ) , 150 / ( 54 * 5 / 18 ) } = lcm ( 15 , 10 ) = 30 sec . answer : a"
Answer: A