A runs twice as fast as B and gives B a start of 50m.How long should the racecourse be so that A and B might reach in the same time?  Pick: A) 75 m . B) 80 m . C) 150 m . D) 100 m . E) none of the above

Rationale: "ratio of speeds of a and b is 2 : 1 b is 50 m away from a but we know that a covers 1 meter ( 2 - 1 ) more in every second than b the time taken for a to cover 50 m is 50 / 1 = 50 m so the total time taken by a and b to reach = 2 * 50 = 100 m answer : d"
Answer: D