Websites like careerride and indiabix are the main resources for Engineering and Computer science mcqs. Most other websites are just plain copies of these websites. Nearly all institutes like FPSC, PTS, NTS, OTS, CTS etc just perform a simple "chappa" from these websites. If you can master the mcqs from these websites, you'll easily pass the written test. Just keep in mind the syllabus relevant to the advertised post from FPSC's website.

Also, dont forget the English portion. Allegedly, you need 13-15 to be considered pass in the whole exam. As such, even if you score the highest in the subject mcqs and your english score is 11/20, you'll fail.

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