Jim runs 50% faster then Bob. In a 1200m race how much of a head start should Bob get to make the race fair? 

My solution:
50%= half
Half of 1200m is 600m
So the answer is 600m
Am I right

nope. 400m head start.

Bob runs 800 m while Jim runs 1200 m.

3 is 50% more than 2.
2 is not 50% less than 3.