NBT common mistakes
NBT · Understand the traps and how to avoid them.
Selects the option that is true in the real world, or true 'in general', rather than the one the passage actually supports - especially on inference and 'the writer would agree' items.
Years of school comprehension tasks reward bringing in background knowledge, and the strongest-sounding option feels authoritative. The NBT rewards evidence inside the text only, so general knowledge becomes a trap.
What to do instead
For every option you are tempted by, find and underline the exact sentence that proves it. If you cannot point to a line, eliminate it. Also distrust options containing absolutes ('all', 'never', 'proves', 'only') unless the passage itself uses that word.
Answers the topic instead of the question - misses the negative or the qualifier in the stem ('which is NOT', 'EXCEPT', 'main purpose', 'the writer implies', 'best').
Under time pressure candidates read the stem once, then jump straight to the options, and the reading brain fills in a familiar question shape rather than the one actually printed.
What to do instead
Read the stem twice and circle the operative word before looking at any option. Restate the task in your own words in the margin ('find the FALSE one'). On negative stems, put a tick or cross beside each option as you evaluate it, and choose the odd one out at the end.
Does percentage work on the wrong base - treats a 20% increase followed by a 20% decrease as a return to the original value, or reads '3 percentage points' as '3%'.
Percentages are learned as procedures ('add 20, subtract 20') and the base is invisible in the numbers, so the second operation gets applied to the original amount rather than the new one.
What to do instead
Write the base down explicitly before computing, and use multiplying factors instead of adding or subtracting amounts: x1,2 then x0,8 gives x0,96, i.e. a 4% net fall. Keep 'percent change' and 'percentage points' as two separate quantities in your working.
Misreads graphs and tables: reads values off the wrong axis, ignores a unit multiplier in the heading ('in thousands', 'R millions'), assumes the vertical axis starts at zero when it does not, or compares bar heights without checking the scale.
The eye processes the picture faster than the labels, and axis breaks or unit multipliers are printed in small type that gets skipped when candidates are behind on time.
What to do instead
Before answering any graph item, physically read aloud the axis titles, the units in the heading, and the value at the origin. Write '1 gridline = ___' at the top of your rough work and convert the two data points you need into the same units before comparing them.
Sets up rates and proportions in the order the numbers appear on the page, without deciding whether the relationship is direct or inverse.
Drilling in cross-multiplication makes it a reflex, so candidates multiply whatever is given without asking what the answer should do as the input grows.
What to do instead
Predict the direction of the answer before calculating ('more workers means fewer days, so my answer must be smaller than 12'), then check that the computed answer matches your prediction. Keep a unit attached to every number and cancel units through the calculation.
'Moves terms across' the equals sign without writing the operation, producing sign errors, dropped coefficients and lost negative signs in multi-step algebra.
This shortcut works on one-step equations done mentally at school, so it is never replaced by written method; it collapses as soon as fractions, brackets or two variables are involved.
What to do instead
One operation per line, with equals signs aligned vertically. Whenever a term changes side, write the inverse operation on both sides rather than relocating it. Expand brackets explicitly on paper - never in your head - and check the final answer by substitution.
Fails to impose or honour restrictions: divides by an expression that could be zero, squares both sides and keeps the extraneous root, cancels a variable, ignores that a length or a count must be positive or a whole number, and never substitutes the answer back.
The question says 'solve for x', so the conditions feel like decoration; candidates optimise for producing an answer rather than for the answer being admissible.
What to do instead
Before solving, write the constraints: denominators not zero, and for word problems 'x is a positive integer' or 'length > 0'. At the end, substitute each candidate back into the original equation (not the squared version) and reject any that fail the constraints.
Tackles geometry, graph and function questions entirely in the head, with no sketch and no marking of the given information.
Drawing feels like wasted time under exam pressure, and candidates overestimate how much of a figure they can hold in working memory while manipulating algebra at the same time.
What to do instead
Redraw the figure in rough work and copy every given onto it - right angles, equal sides, parallel marks, coordinates, the value asked for as a '?'. For function questions, sketch the parent graph and transform key points rather than reasoning abstractly.
Reaches reflexively for a calculator, or freezes when arithmetic must be done by hand; weak on fraction-decimal-percentage conversions, squares and two-digit multiplication.
School and daily life allow a calculator, and it is easy to assume the NBT does too. Nobody has drilled mental arithmetic recently, so routine computation becomes a time sink and an error source.
What to do instead
Practise without a calculator: squares to 20, the common fraction-decimal-percentage table, two-digit multiplication, and division of decimals. Before computing, cancel common factors and simplify the expression so the arithmetic is small - a well-simplified expression rarely needs long division.
Burns eight to ten minutes on a single early question, then meets the back half of the paper with almost no time left and leaves items blank.
Sunk cost ('I've nearly got it') plus the assumption that every question deserves equal effort. Early questions feel like they must be solved before moving on.
What to do instead
Apply a 90-second rule: if no route is visible, mark the item and move. Work in two passes - everything you can do quickly first, then the marked items. Never leave a blank, since there is no penalty for a wrong answer, and reserve the last few minutes for those guesses.