You have a 1000cc volume, 720cc displaces water, it tells you what the water weighs. Now 280cc displaces oil, it tells you what the oil weighs. Find the weight of both displacements and add them together for the total weight. You should be able to work it with this. Also you put .78 in your equation for water volume, it should be .72
Since we really don't know how big the universe is what I suggest you do is take the size of the observable universe and then use the inverse square law along with the average photons the sun outputs in whatever given amount of time you want and then use the average density of matter in our universe and use all of those variables to calculate your answer.
That likelyhood changes over time, in the early universe when everything was dense the mean free path of a photon was rather short, while in the meantime it has grown to approximately 10 billion lightyears, see
Paul Davies wrote: The mean free path is
about a Hubble radius (10²⁸ cm = 10²³ km).
Wikipedia wrote: The mean free path of a photon
We will consider the case of real transport with a given flow rate $J=\rho u$. We assume that all compressors are identical, capable of maintaining a given air flow. Specifications: the flow velocity is limited by the condition $1\le u\le 10$ m/s. It is necessary to determine how many compressors are needed and how to optimally position them when ...
No. If the object has a compressibility much less than water (nothing is perfectly incompressible) it would only sink part way. At a depth of 10,000 ft, the water would be about 1.4% denser, assuming temperature remained constant.
The term negative charge density is incorrect. By definition: charge density is the amount of charge per unit length (linear charge density), unit area (surface charge density) or unit volume (volume charge density). Corresponding units are: $C/m$, $C/m^2$ and $C/m^3$ respectively. There can not be less than zero charge, therefore charge density can not be ...