OGE Informatics common mistakes
OGE Informatics · Understand the traps and how to avoid them.
When converting a number from decimal to binary or back, the candidate drops or misplaces a digit because they write the remainders top-to-bottom instead of reversing them, or they stop dividing before the quotient reaches zero.
The repeated-division method is memorized as a sequence of steps but the direction of remainder collection is not understood, so the final string is assembled in the wrong order under time pressure.
What to do instead
After every conversion, verify by re-expanding the result as a sum of powers of two and checking it equals the original decimal. Practise 10 conversions in each direction and always write remainders in a column, then read them upward.
The candidate computes the information volume of a text or image message using the wrong unit relationship, mixing bits, bytes and KiB with factors of 1000 instead of 1024, or forgetting that 1 byte = 8 bits when converting a bit count to bytes.
Everyday use of 'kilo' as 1000 conflicts with the binary prefix convention, and the bit-to-byte step is easily skipped when the formula result is already a large number.
What to do instead
Write the unit chain explicitly on scratch paper (bit -> byte /8 -> KiB /1024 -> MiB /1024) and substitute numbers into it rather than converting mentally. Check that a character in a single-byte encoding is stated as 8 bits or 1 byte before multiplying.
When tracing a loop with a counter or accumulator, the candidate evaluates the condition once and assumes the loop body runs a fixed number of times, missing that the counter changes inside the body or that the condition is checked before the first iteration.
Loops are read as prose ('repeat until done') rather than simulated step by step, so off-by-one errors and pre-condition versus post-condition differences go unnoticed.
What to do instead
Build a trace table with one column per variable and one row per iteration, filling in values before and after the body. Mark the condition check as its own row so the final failed check is counted.
The candidate confuses assignment with comparison, or misreads the direction of assignment, when predicting the output of a short program (for example treating 'x := x + 1' as an equation to solve).
Mathematical training makes '=' look like equality, and pseudocode notation varies between textbooks, so the meaning of the operator is inferred rather than applied.
What to do instead
Before tracing, rewrite each assignment as 'new value of variable = ...' in words. Practise distinguishing ':=' (store) from '=' (compare) and check the final value of every variable, not just the printed one.
When reading a flowchart, the candidate follows the arrows visually but ignores the branch labels (Yes/No) on a decision diamond, producing a trace that takes the wrong path at the first condition.
Flowcharts are skimmed as pictures; the small text on the branches is treated as decoration rather than as the control condition.
What to do instead
Annotate each decision diamond with the actual value of the tested variable at that moment, then state aloud which branch is taken. Trace at least two full passes through any loop in the chart.
The candidate builds a spreadsheet formula with relative references that shift unexpectedly when filled or copied, or omits the '$' anchors on a lookup range, so totals silently reference the wrong cells.
Relative addressing is the default and the formula looks correct in the first cell, so the error only appears after filling down, and the displayed result may still be a plausible number.
What to do instead
Decide explicitly which references must stay fixed and write them with $ before filling. After filling, click two or three cells in the middle and end of the range and read the formula bar to confirm the references point where intended.
The candidate answers a database or search query by scanning the table and guessing, instead of applying the logical condition, so records that satisfy only part of a compound AND/OR condition are wrongly included or excluded.
Natural-language reading of 'and' is loose, and multi-condition filters are evaluated intuitively rather than by checking each record against every clause.
What to do instead
Rewrite the condition as a checklist of atomic tests and evaluate each record against all of them, marking pass/fail per clause. For OR, stop at the first true clause; for AND, stop at the first false one.
The candidate treats a file's extension as proof of its content or assumes a folder path is absolute when it is relative, so they misidentify file type or resolve a path to the wrong location.
Extensions are learned as labels ('doc means text document') without the idea that they are conventions, and the root-versus-current-folder distinction is not modelled.
What to do instead
For path questions, draw the folder tree and walk from the stated starting point one level at a time, writing the current location after each step. For file-type questions, base the answer on the described content, not on the extension alone.
The candidate evaluates a network or internet scenario by assuming a URL identifies a person or that a secure padlock guarantees trustworthy content, and so misjudges phishing or safe-use questions.
The padlock and domain name are read as trust signals in general rather than as narrow technical facts (encrypted connection, registered name), and the distinction between protocol, domain and path is fuzzy.
What to do instead
Learn the URL anatomy (protocol, domain, path) and the rule that HTTPS certifies the connection, not the honesty of the site owner. For each safety scenario, name the specific risk (credential theft, malware, impersonation) before choosing an answer.
The candidate answers a practical text- or spreadsheet-editing task by describing the steps instead of performing them, or performs them but leaves the file unsaved or in the wrong format/location, so the work is not credited.
Exam technique trained on multiple-choice carries over into practical tasks, and the save step is treated as an afterthought rather than part of the task requirement.
What to do instead
Rehearse the full practical routine: open the given file, make the edit, save under the required name and format in the required folder, then reopen it to confirm. Treat the save-and-verify step as a scored action, not cleanup.