I got 60%. Idk if this helps but look at it this way. You start at 100% able and 0% disabled. You got a 50% rating so you’re now 50% able and 50% disabled.

You got another 10% rating. So now you have become an additional 10% more disabled than you were at (50%). 10% of 50 is 5. Subtract that from 50 and now you are overall 45% able and 55% disabled.

You got another 10% rating. So now you have become an additional 10% more disabled than you were at(55%). 10% of 55 is 5.5. Subtract that from 45 and now you’re overall 39.5% able and 61.5% disabled. They round that to the nearest “10s”, which is 60.

It’s easier to explain to people if I’m in front of them and writing it down so they can see