From Chris' perspective Bob is travelling with 1.5*108 m/s in direction a. Angelica is also travelling with 2.4*108 m/s in direction a. From Bob's perspective Chris is travelling with 1.5*108 m/s in direction b (The opposite of x). Angelica is travelling with 1.5*108 m/s in direction a. They all have a mass of 1 I am pretty sure these numbers are right. I used w = (u+v)/(1+(u*v)/(c2)) To calculate the relative speeds. I used the calculation in the picture to calculate the Ek of Bob. I also calculated the Ek of Angelica, all from chris' perspective. Now the outcome that I was expecting was that Bob's Ek would be half of Angelica's Ek when looking from Chris' perspective. Because Angelica is also travelling with 1.5*108 m/s when measured from Bob's perspective. Why does this not count up? I am sorry if a skipped a few vital steps. All of my special relativity knowledge comes from self-studying. We don't get this in school. Thank you in advance.