The time for a project to be completed is shortened from the original 30 days to 20 days. How many points has the work efficiency been improved?

The time for a project to be completed is shortened from the original 30 days to 20 days. How many points has the work efficiency been improved?

(1/20-1/30)÷1/30
=1/60÷1/30
=1/2
A: work efficiency has been increased by 1 / 2