Given the task definition and input, reply with output. You are given a math word problem and you are supposed to apply addition or subtraction mathematical operators on the numbers embedded in the text to answer the following question and then only report the final numerical answer.

A spaceship traveled 0.5 light - year from Earth to Planet X and 0.1 light - year from Planet X to Planet Y . Then it traveled 0.1 light - year from Planet Y back to Earth . How many light - years did the spaceship travel in all ?

0.7