The cheapest is by train or bus (plus a ferry), especially if you book well in advance. Fares start from about £25.
That will depend on where you are coming from. You may even need a visa, but that is something you would have to check with your local authorities. As a general rule, always bring a passport when...
Aberdeen to Glasgow Queen Street is approximately 2 hours and 40 minutes. The exact time depends on which service is used.
About 3½ to 4 hours
A direct flight from Paris, France --> Glasgow, Scotland would take about 2 hours.
Visit Kelvingrove Park in Glasgow, UK
Visit the Clyde Arc in Glasgow, Scotland
Cultural and Architectural Sites in Glasgow, Scotland
Visit the Cultural and Architectural Sites in Glasgow, Scotland