Question

If the mass of earth were 2 times the present mass, mass of moon were half the present mass and moon were revolving around the earth at same present distance time period of revolutionof moon would be in days?

Answer 1

Time taken for one orbit is inversely proportional to the square root of the mass of the central body (earth in this case).
Therefore the new time for 1 orbit is equal to 1 / √2 times the original time.
The original time for one orbit is 27 days