What is the most efficient and economical way to do Giverny and Versailles in one day from Paris?
Coach tour. Google will yield several results for companies that do this.
You can't really do this by public transport, as Vernon and Versailles are on different train lines out of Paris. You would have to return to Paris to get from Giverny to Versailles.
thanks you so much
Beside the different direction, you need to allow at least 2/3 of a day for a proper Versailles visit.