GNFS Aptitude Test flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Percentage change formula

Divide the difference by the original value, then multiply by 100. Always divide by the starting figure, not the final one, or the sign and size will be wrong.

Successive percentage changes

Convert each change to a multiplier and multiply them. A 20% rise then a 15% fall gives 1.20 × 0.85 = 1.02, a net rise of 2%, not 5%.

Harmonic mean for average speed

For equal distances travelled at speeds a and b, average speed is 2ab divided by (a + b). The simple mean overstates it whenever the speeds differ.

Combined work rate

Add rates as reciprocals of completion times. If A takes 4 hours and B takes 6, together they need 1 divided by (1/4 + 1/6), which is 2.4 hours.

Ratio sharing unit value

Divide the total by the sum of the ratio parts to get one part, then multiply each term. For 3:5 sharing of 64, one part is 8.

Profit percentage base

Profit percentage is measured against cost price: (selling price minus cost price) divided by cost price, times 100. Margin, by contrast, uses selling price.

Contrapositive equivalence

'If P then Q' is logically equivalent to 'if not Q then not P'. The converse, 'if Q then P', and the inverse are not equivalent and are common traps.

Necessary versus sufficient condition

A necessary condition must hold for the outcome; a sufficient condition guarantees it. 'Required for' signals necessary, 'guarantees' signals sufficient.

Unless translation

The sentence 'unless P, Q' means 'if not P, then Q'. It does not assert that P occurs, only that Q holds whenever P fails.

Only if translation

'Q only if P' means 'if Q then P', making P necessary for Q. It does not mean P is sufficient, so Q need not follow from P.

Scope-word distractors

Answer choices often fail by shifting quantifiers: all versus some, always versus sometimes, must versus may. Compare these words between passage and option before choosing.

Valid versus true

Validity concerns structure: the conclusion must follow from the premises. Truth concerns content. A valid argument with false premises can reach a false conclusion.

Analogy relation types

Check function, part-to-whole, category membership, cause to effect, degree, and worker to tool. The correct pair must share the same specific relation, not a vague association.

Negation test for assumptions

Negate the candidate assumption. If the argument's conclusion collapses under the negation, the statement was genuinely required; if it survives, it was not an assumption.

Syllogism diagram test

Draw premises as overlapping sets and test the conclusion in every consistent arrangement. A conclusion is forced only if no valid diagram contradicts it.

Alternating frame series

In abstract sequences, odd-numbered and even-numbered frames may follow separate rules. Split the series into two before inferring a single transformation.

Rotation step rule

Track one element across frames and count its steps around the perimeter or its degrees of turn. A constant step confirms rotation rather than reflection or swapping.

Odd-one-out justification

State the exact shared property of four options, such as all having one enclosed region. The fifth must fail that precise property, not merely appear unusual.

Constrained-entity-first ordering

In seating or scheduling puzzles, place the entity with the most constraints first, then those with two constraints, then fill remaining positions by elimination.

Transposition detection

Compare long digit or letter strings in fixed blocks of three or four. Adjacent swapped characters are the most common error and are missed in left-to-right reading.

Confusable character pairs

Watch for zero versus letter O, one versus l and I, five versus S, two versus Z, and rn versus m. These substitutions are inserted deliberately in accuracy items.

Date convention check

Confirm whether dates use day/month/year or month/day/year before calling a mismatch an error. The same string can be valid under one convention and invalid under the other.

Rounding rule precedence

Apply the rule stated in the item, such as round half up, half to even, or truncate. Stated rules override personal habit, and half values are the usual test point.

Unit mismatch error

Errors are often hidden in units rather than digits: kilograms against grams, kilometres against metres, or pounds against dollars. Verify units before checking arithmetic.

Two-route total check

Verify a table total by summing columns and separately summing rows, then compare both results with the stated grand total. Agreement on both routes confirms accuracy.

Expected value rule

Multiply each outcome's value by its probability and add the results. Choose the highest expected value only when the decision maker is risk-neutral.

Break-even volume

Divide fixed costs by the difference between unit price and unit variable cost. Below this volume the option makes a loss; above it, each extra unit adds contribution.

Sunk cost irrelevance

Costs already incurred cannot be recovered and must be excluded from forward decisions. Only future costs and benefits that differ between options are relevant.

Opportunity cost definition

The value of the single best alternative forgone when a choice is made. It is not the sum of every rejected option, only the most valuable one.

Scarce resource contribution rule

When a resource is limited, rank options by contribution per unit of that resource, not by contribution per unit sold. The highest unit margin may waste the constraint.

Truncated axis distortion

A y-axis that does not start at zero exaggerates differences between bars. Check the origin before judging the size of any apparent change.

Weighted average of group means

Combine group means by weighting each by its group size, then divide by the total size. A simple mean of the means misstates the overall figure when groups differ in size.