Two trains start from P and Q respectively and travel towards each other at a speed of 50 km/hr and 40 km/hr respectively. By the time they meet, the first train has travelled 100 km more than the second. The distance between P and Q is :
Choose the correct choice from the following answers
A) 500 km B) 630 km C) 900 km D) 660 km E) none

Rationale: "sol . at the time of meeting , let the distane travelled byb the second train be x km . then , distance covered by the first train is ( x + 100 ) km ∴ x / 40 = ( x + 100 ) / 50 ⇔ 50 x = 40 x 4000 ⇔ x = 400 . so , distance between p and q = ( x + x + 100 ) km = 900 km . answer c"
Answer: C