Here are some of the laptops that you can checkout for under 20,000 Rs.
HP 245 G4,P1b38PA
This laptop has thee 14 inch display with 1080p Full HD support. It has AMD A6 Quadcore processor. For most of the office and student use this can be enough processing power. You get 4GGB RAM along with 500 GB HDD. The machine seems to have FreeDOS on it. So you may have to install Windows 10 or other OS of your choice. You can get the machine at the price of : 19,150 on Amazon. Check the device here: http://www.amazon.in/HP-245-P1b38PA-Inch-Quadcore/dp/B01FSSZIMS/
Asus Eeebook E402SA-WX014T
This laptop is 14 inch display with 1366x768 resolution. It has 2GB RAM and 32GB this is more of suitable for the student usage. Though you may need additional disk space. For which you can use the external drive or USB HDD. It has 2.16GHz Intel Celeron N3050 processor which is fast enough for the regular usage. Also it has Windows 10 home installed. Compared to other devices this one is lightweight and compact to use. You can get this machine at the price : 16,490 Rs. You can get it through Amazon. http://www.amazon.in/Asus-Eeebook-E402SA-WX014T-Integrated-graphics/dp/B01C70I8BS/
Acer Aspire ES1-521
This model from Acer has the 15.6 inch display. It has 4GB RAM and 1TB HDD. You may find the machine to have a good AMD APU Dual Core. Machine has the Linux installed on it. So if you don't want it then you can switch to Windows 10. The machine costs around 18,377 Rs on Amazon. You can check out the machine on Amazon india heree: http://www.amazon.in/Acer-Aspire-ES1-521-NX-G2KSI-024-Diamond/dp/B01C5P1BXM/
Micromax Neo PQC LPQ61407W
This model from Micromax is more suitable as a netbook. Considering it is more lightweight than regular laptop. It has 14.1-inch display. The machine has the Pentium N3700 processor. The machine has the 4GB RAM and 500 GB hard disk. The machine has Windows 10 OS installed. It is a very good laptop at this price. It costs 17,990 Rs on Amazon India. You can find it on this page : http://www.amazon.in/Micromax-LPQ61407W-14-1-inch-Integrated-Graphics/dp/B01KO18NTE/
These are the models that fit your budget and requirement.