Explaination of beta + decay in layman language

[Suyash Singh]

QUESTION:
I read in book that in beta + decay proton decays to neutron

But i can't understand how it is possible if proton mass is less than neutron mass.I read on net but it says 'quarks' and 'd u p' things which i don't study about currently.

Also why it only happen inside nucleus?What does nucleus do?
EQUATION:
proton>neutron + positron + neutrino
ATTEMPT AT SOLUTION:
I know that beta + will make atomic number decrease by 1.
I know binding energy is from mass defect.

 

[Nugatory]

Remember Einstein's famous $E=mc^2$: mass is a form of energy, so when you say that the proton mass is less than the neutron mass you're really saying that you have to add energy to turn a proton into a neutron. Thus, an isolated proton cannot decay into a neutron, just as you're expecting. But some unstable nuclei may end up with less mass/energy if one of their protons decays into a neutron, and these are ones that will undergo beta+ decay. The total energy of the nucleus is reduced by an amount sufficient to allow the proton to neutron transition.