A and B go around a circular track of length 200 m on a cycle at speeds of 36 kmph and 72 kmph. After how much time will they meet for the first time at the starting point?	Choose the correct answer
A) 120 sec	B) 198 sec	C) 178 sec	D) 20 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 { 200 / ( 36 * 5 / 18 ) , 200 / ( 72 * 5 / 18 ) } = lcm ( 20 , 10 ) = 20 sec . answer : d"
Answer: D