Rs. - INR (Indian rupee). At least be thankful that he's not posting the new symbol for rupee that they invented recently - .
1 USD = 44-45 INR. You guys are both wrong - the OP for not explaining correctly, and GeekApproved for bashing him right away instead of using Google to expand his knowledge (takes 1 min, lol).
20000 Rs. Tight. Don't expect any serious gaming with this budget, but let me try and help.
CPU: Intel Core i3-2100 (Rs. 5500)
Mobo: Intel DH67BL (Rs. 5000)
RAM: Corsair/Kingston 1333 MHz 2 sticks, each 4GB (Rs. 2500)
Graphics: onboard. Or find a used PCI-E graphics card for free from a friend.
PSU: Huntkey 450W or 550W (Rs. 2500 to 3000)
Screen: excluded, or exceed your budget with Samsung 21'' LED (Rs. 9000) if you don't have a screen
Case: personal preference, this system won't need serious cooling, but you can grab Cooler Master Elite 370 for Rs. 3000 if you can get these lazy asses to find it for you (had to convince the PC hardware shop people to look for it instead of simply denying the availability).
In the future, I advise you to be a bit more specific - and not only here. I've seen this attitude from Indian people both on Tom's and IRL way too much - really, there's no need to be like that.