How can you measure the mean density of a neutron star

[renmoresnow]

How can you measure the mean density of a neutron star if your only told its mass is three times that of the Sun?

 

[amarante]

You know it's mass, but you can also estimate the radius of a neutron star.

 

[Matterwave]

You can use an estimate for the size. Neutron stars are around 12km in radius. Not every neutron star is this radius, of course, but at least you can get an estimate.