Subject: mathqa
Question: a ’ s speed is 20 / 13 times that of b . if a and b run a race , what part of the length of the race should a give b as a head start , so that the race ends in a dead heat ?
Option: 
A: 7 / 20
B: 3 / 10
C: 1 / 10
D: 3 / 17
Answer: A