Thermodynamics which equation is correct

[pokie_panda]

Homework Statement

Calculate the energy which has 15.5% occupancy probability for copper at T=295. Assume, Ef = 7.00eV for copper.

I seen two equations which one is correct

1
_____________
exp(E- Ef / kT)


or
1
_____________
1+(exp(E- Ef / kT))

 

[vela]

That's a question you should be able to answer on your own. Neither of those is an equation as no equal sign appears anywhere. Where did you get these expressions from? What does your textbook say?