Option 1 - Deduction u/s 80GG :
Deduction will be lower of the following:
a. R.s 2000/- per month;
b. Rent paid in excess of 10% of total income (TI) i.e. 4700-(10% of TI); or
c. An amount equal to 25% of TI.
One of the conditions for claiming deduction under this section is that the assesse should not get House rent Allowance from the employer.
Option 2. In case your friend is receiving HRA assuming him to be a salaried employee, then exemtion u/s 10(13A) can be claimed as follows:
Exemption will be lower of the following:
a. Actual HRA received;
b. Rent Paid less 10% of Salary i.e. 4700-(10% of Salary) ; or
c. 50% of Salary if PG in Delhi, Mumbai, Chaeenai or Culcutta ; 40% of Salary if PG at any other place.
Salary for the purpose of HRA calculation includes dearness allowance it the terms of the employment so provide but excludes all other allowances n perquisites.
Either of option 1 or 2 can be excercised at a time depending on the facts.
Hope the above will suffice.