A runs twice as fast as B and gives B a start of 42m.How long should the racecourse be so that A and B might reach in the same time?  Choices.
A) 75 m.	B) 80 m.	C) 84 m.	D) 100 m.	E) None of the above
ratio of speeds of a and b is 2:1   b is 42m 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 42m is   42/1= 
<gadget id="calculator">  42/1</gadget>
<output>42</output>
42m   so the total time taken by a and b to reach=2*42= 
<gadget id="calculator">2*42</gadget>
<output>84</output>
84m   ANSWER:84 m.
<result>C</result>
A runs twice as fast as B and gives B a start of 42m.How long should the racecourse be so that A and B might reach in the same time?