What is the CDS examination?
The Combined Defence Services Examination (CDS) is conducted by the Union Public Service Commission (UPSC) twice a year to select graduates for officer training at four academies — the Indian Military Academy (IMA) at Dehradun, the Indian Naval Academy (INA) at Ezhimala, the Air Force Academy (AFA) near Hyderabad and the Officers Training Academy (OTA) at Chennai. It is one of the principal routes to a permanent or short-service commission in the Indian Armed Forces.
Selection has two main parts: a written examination and a Services Selection Board (SSB) Interview, followed by a medical examination. For IMA, INA and AFA the written exam has three papers — English, General Knowledge and Elementary Mathematics — of 100 marks each (300 in all). OTA candidates take only English and General Knowledge (200 marks) and no mathematics paper. Every wrong answer carries a one-third negative penalty, so accuracy matters as much as speed.

