Empirical --> Chemical Formula using molar mass somehow

[s3a]

A compound is found to have the empirical formula P2O5, and a molar mass of 283.88 g/mol. What is its molecular formula?

Answer: P4O10

I have no idea how to do this. To the best of my abilities, here is what I've done:

P2O5 = 110.97076g/mol (Periodic Table)

(283.88 g/mol)/(110.97076 g/mol) = 2.558

(2.558)(the subscripts from empirical formula)

(2.558)(2) = 5.116 (instead of 4)
(2.558)(5) = 12.791 (instead of 10)

Any help would be greatly appreciated!
Thanks in advance!

[Sonic]

A compound is found to have the empirical formula P2O5, and a molar mass of 283.88 g/mol. What is its molecular formula?

Answer: P4O10

I have no idea how to do this. To the best of my abilities, here is what I've done:

P2O5 = 110.97076g/mol (Periodic Table) Sonic: Check this part here

(283.88 g/mol)/(110.97076 g/mol) = 2.558

(2.558)(the subscripts from empirical formula)

(2.558)(2) = 5.116 (instead of 4)
(2.558)(5) = 12.791 (instead of 10)

Any help would be greatly appreciated!
Thanks in advance!

I made the atomic mass of P: 30.974 (3dp) and that of O: 15.999 (3dp)
(Source: http://www.webelements.com/)

P2O5 = 2*30.974 + 5*15.999 = 141.943

If you take the value I calculated and do what you did thereafter you should arrive at the answer.

As a note with this kind of problem it's rarely likely to be exactly an integer but if it's close enough then it's ok to round. For example 1.999 can be assumed to be 2 for this purpose