Mona and Sona go around a circular track of length 400 m on a bike at speeds of 18 kmph and 36 kmph. After how much time will they meet for the first time at the starting point?  Choose the most appropriate option:
A) 120
B) 80
C) 60
D) 136
E) 150
Time taken to meet for the first time at the starting point   = LCM { length of the track / speed of monA , length of the track / speed of sona}   = LCM { 400/ (18 * 5/18) , 400/ (36 * 5 /18) }   = LCM (80, 40) = 80 sec.   Answer: 80
<result>B</result>
Mona and Sona go around a circular track of length 400 m on a bike at speeds of 18 kmph and 36 kmph. After how much time will they meet for the first time at the starting point?