During one start, an electrically powered fairground ride receives 2.5 MJ2.5\ \mathrm{MJ}2.5 MJ of energy and transfers 1.5 MJ1.5\ \mathrm{MJ}1.5 MJ usefully to its kinetic energy store.
After a modification, the energy dissipated during each start is 40% less than before. The total energy supplied during each start remains the same.
Calculate the efficiency of the ride after the modification.
Give your answer as a percentage.