Time and distance

TIME & DISTANCE :

• Distance = Speed * Time
• 1 km/hr = 5/18 m/sec
• 1 m/sec = 18/5 km/hr
• Suppose a man covers a certain distance at x kmph and an equal distance at y kmph. Then, the average speed during the whole journey is 2xy/(x+y) kmph
• Likewise, travelling 3 equal distance with speeds x,y and z, average speed = 2xyz / (xy+yz+zx)
• Time taken after meeting (same distance):-
  if 2 persons starts journey from A & B and move towards each other and meet at C, after meeting they reach opposite points in x & y hrs respectively.
  
  
  then speed before they meet is  √y : √x
  Q. Seeta start her journey from Mumbai towards Pune at speed of  20 kmph & her sister Geeta starts her journey from Pune towards Mumbai at speed of 30 kmph. They meet at Lonavala. What is ratio of time taken by them to reach their destinations after they meet ?
  (1) 9:4 (2) 2:3 (3) 3:2 (4) 1:1 (5) Data insufficient
  Solution :-
  Speed before they meet is x:y i.e. 20:30
  time after they meet will be y²:x² = 900 : 400 = 9:4. Hence answer option 1.