KE of Gas Molecules: n, KbT, U, and 3/2R

[RougeSun]

I know that KE=3/2KbT, but doesn't the KE of gas molecules also equal U=3/2nRT? When do I use which? And also for the second equation if it is for a monoatomic gas, n=1, why isn't the n deleted?

 

[Vanadium 50]

Look at the relationship between k, R and Avagadro's number.

 

[RougeSun]

K=R/(Avagadro's Num), so 3/2*R/(Avagadro's Num)*T=3/2nRT
getting rid of the same constants I get 1/(Avagadro's Num)=n