Computer Science: Fundamentals, Logic, Data and Web Basics
What this domain tests
Computer Science in the PSEB Senior Secondary Computer Application paper checks whether you can move between theory and hands-on tasks: positional number systems, Boolean algebra, operating-system file handling, word processing, spreadsheets, SQL, networking and basic HTML. Expect direct conversion questions, formula problems and short SQL or markup outputs.
Core rules to keep straight
- Binary, octal and hexadecimal use positional weights. For binary, integer weights are 8, 4, 2, 1; fraction weights are 1/2, 1/4, 1/8.
- Boolean identities: A + A' = 1; A·A' = 0; De Morgan: (A+B)' = A'·B' and (A·B)' = A' + B'.
- Spreadsheet references: A1 is relative, $A$1 is absolute, $A1 locks the column, A$1 locks the row.
- SQL logical order is FROM → WHERE → GROUP BY → HAVING → SELECT → ORDER BY. WHERE filters rows; HAVING filters groups.
- HTML elements nest properly, attributes go in quotes, and void elements such as
do not need closing tags.
Worked example
Convert 1101.101₂ to decimal and hexadecimal. Integer part: 1×8 + 1×4 + 0×2 + 1×1 = 13, which is D in hex. Fraction: 1×0.5 + 0×0.25 + 1×0.125 = 0.625. Combined decimal value = 13.625; hexadecimal = D.A. The reasoning is that each digit is multiplied by its positional weight, and the fraction weights halve at each step.
Traps that cost marks
- Forgetting the negative weight of the sign bit in 8-bit two's complement: 10000000₂ represents −128, not −0.
- Writing WHERE COUNT()>2 instead of HAVING COUNT()>2.
- Copying =B2*C2 down a column when C2 should be a fixed rate such as $C$2.
- Treating a text-formatted number as numeric in a spreadsheet; it will not sum correctly.
- Using a closing tag for
or in strict HTML questions.