Week 1 · ACCURACY FIRST · 10–15 hrs

Foundations in arithmetic, CR & DI

Arithmetic fundamentals and estimation

Quantitative

GMAT Focus uses this topic as scaffolding, not as a destination. A bare computation is not the deliverable. What is tested is controlled approximation: deciding whether exactness is required at all, and knowing the error you are carrying when it is not. In Data Sufficiency, the skill is stopping the moment an expression's size, sign, or parity settles the question.

Disguises: answer choices spaced so widely that one rounded division eliminates three of them; "must be a multiple of" questions where only divisibility structure matters; digit and units-digit questions; and rate, percent or weighted-mix word problems whose numbers are ugly on purpose.

Three decisions separate the correct answer from the tempting one. Measure the answer choices before computing: if they differ in the leading digit, estimate; if they differ in the second, compute exactly. Track the direction of your approximation — whether it over- or under-states the true value is what picks the choice, not its size. In DS, stop as soon as the statement can no longer change the answer.

The mechanical way strong candidates lose points: chaining rounded intermediates so error compounds across steps, then finding two choices sitting inside their own uncertainty band. Round once, at the start, or not at all; carry exact values forward.

Worth having in memory: for consecutive integers beginning at 1, the sum of the first $n$ terms is $\frac{n(n+1)}{2}$.

Fractions, decimals and percents as one system

Quantitative

GMAT Focus does not ask you to convert $\frac{3}{8}$ into a decimal. It asks you to notice that $\frac{3}{8}=37.5\mathrm{\%}$, that the answer choices are written as fractions, and that multiplying by $\frac{3}{8}$ is therefore cheaper than multiplying by $0.375$. The topic is one quantity wearing three costumes, and the exam tests whether you pick the cheapest costume for the operation in front of you.

The disguises: data-sufficiency statements give one value as a fraction and another as a percent; a word problem says "reduced to $\frac{1}{4}$" when you expect "reduced by $\frac{1}{4}$"; a chart labels in percent while the question asks for a count.

Two decisions decide most questions. First, choose the representation that makes the next operation one step: percent for a quick multiplier, fraction for exact cancellation, decimal only for ordering or adding. Second, successive percent changes multiply, never add — a rise of $20\mathrm{\%}$ then a fall of $20\mathrm{\%}$ is $1.2\times 0.8=0.96$, a $4\mathrm{\%}$ net fall.

The mechanical loss is precision drift: rounding $0.375$ to $0.38$ mid-chain, then choosing the answer choice built from that error. Keep one exact form until the final line.

Have in memory: $\text{new}=\text{old}\times (1\pm r)$ with $r$ as a decimal, so $0.4\mathrm{\%}$ means $r=0.004$.

Ratios and proportions

Quantitative

GMAT Focus rarely asks you to define a ratio. It asks you to translate a verbal relationship into a scale-free comparison, then decide what absolute anchors the scale. The exam's favourite move is to give you a ratio and one real quantity, or to hide a ratio inside a rate, a mixture, or a percentage.

Disguises: 'for every 3 ... there are 5 ...', 'per', 'out of', 'the same proportion', and any rate (miles per gallon, students per teacher). In Data Sufficiency, the question may ask for a fraction of a total, a ratio, or an absolute; the statements will mix ratio and absolute information, and you must know which is which.

Three decisions separate correct from tempting. First: is the ratio part-to-part or part-to-whole? Boys:girls is part-to-part; boys:students is part-to-whole. Second: do not treat ratio numbers as counts. Write $A=mk$, $B=nk$. Third: check what is asked — a ratio statement alone cannot yield an absolute; an absolute alone cannot yield a ratio unless the other part or the total is known.

The mechanical loss: reversing the order ($B\mathrm{/}A$ instead of $A\mathrm{/}B$) or adding parts to form a total when the ratio is part-to-part but the question asks for a part-to-whole fraction. At this stage, write the multiplier explicitly rather than doing ratio arithmetic in your head.

Memory: if $A:B=m:n$, then $A=mk$, $B=nk$, and $A\mathrm{/}(A+B)=m\mathrm{/}(m+n)$. Use it whenever you need to convert between a ratio and actual counts or a fraction of the total.

Illustration: flour:sugar $=5:2$ and 15 cups flour gives sugar $=2\times (15\mathrm{/}5)=6$ cups.

Critical Reasoning: finding the conclusion

Verbal

On GMAT Focus, the conclusion is the claim the rest of the passage exists to support. The exam rarely labels it. It appears as a recommendation, a prediction, a causal claim, or a rebuttal to an opposing view, and it can sit first, last, or mid-paragraph.

The two decisions that separate right from tempting:

Is the statement doing the supporting or receiving it? Insert "therefore" between candidate pairs. If statement A therefore statement B reads as a coherent argument, B is the conclusion. This test works only when both statements belong to the same argument.

Whose claim is it? A vivid opposing view is not the author's conclusion. The author's conclusion is what the author wants you to accept; opposing views are premises in a rebuttal. Also, distinguish the main conclusion from an intermediate conclusion, which is supported by other premises and itself supports the final point.

You will lose points mechanically by grabbing the last sentence, or the most extreme sentence, without checking what supports what. In an argument ending "Clearly, the policy will fail," that sentence is often the conclusion—but verify by asking what the author would say if challenged with "why?" The answer reveals the premises.

Compact illustration: "The new toll will reduce congestion; after all, similar tolls cut traffic elsewhere." The conclusion is the first clause.

Reading tables and charts without assuming

Data Insights

Data Insights rarely asks you to construct anything. It hands you a table or a chart and asks for one value, one comparison, or one yes/no condition — which means almost every point on this topic is lost the moment you start reading the picture instead of the labels.

What is actually tested is the chart's apparatus: axis ranges and tick spacing, units, the footnote that redefines a denominator, and whether a series is a count, a rate, a running total, or an average. Graphics Interpretation gives you a handful of drop-downs, each usually settled by one number read off correctly. Table Analysis gives you a sortable table and a condition — sorting is a tool you apply, not a property of the data, and a table that arrives unsorted punishes anyone who assumes otherwise.

The disguises: a non-zero baseline; a second series on a right-hand axis with its own scale; two legend entries a shade apart; a 'total' row drawn from a different population than the rows above it; a chart in thousands with options in millions; adjacent columns expressed as percentages of different bases; an x-axis with a missing year.

Three decisions separate right from tempting. Read axes, units and footnotes before any comparison. Establish whether the question wants a level, a change, or a ratio — and against which base. If the chart shows shares, recover counts before comparing groups.

Strong candidates lose here by answering from visual impression: the taller bar, the steeper slope, the obviously bigger group. It bites hardest on "largest increase" questions where the x-axis is unevenly spaced.

Keep one relation: $\text{segment value}=\text{segment share}\times \text{category total}$, valid only when the share is taken of a total the chart actually states.

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