I look at it this way. I ride my conventional bike 20 miles during an average workout.
With an average load, my ebike is capable of doing 20 miles on a single charge using electric power alone.
During an average ebike workout, I ride 50 miles on a single battery charge.
The bike provides the energy for 20 of those miles and my pedaling is responsible for the remaining 30.
This means I'm providing the energy for an additional 10 miles during each outing, a 50% increase.