SSC CGL Tier I carries -0.5 for every wrong answer. That single number decides how many questions you should attempt.
If your accuracy on "confident" questions is 90% and on "guesses" is 40%, every blind guess has a negative expected value. Attempt only what you can justify.
The practical rule: mark-for-review anything you are below 60% sure of, come back with the time left, and leave the rest. Most toppers attempt 88–92 of 100 — not all 100.