Correct Errors, Recall Methods, and Update Your Weakness Log

Hello! Your last lesson was a 40-minute set of ten CAT previous-year QA questions on numerical operations and percentages. You recorded not only answers, but also skips, uncertain bases, and questions that took too long. Today you will turn that record into corrections you can use: reattempt the questions that exposed a weakness, recall the methods without notes, and update a QA-only weakness log.

Allow 45 minutes for this block. Together with the previous timed set, it forms an 85-minute end-of-module revision session. Keep your scratch work and answer record beside you; they are more informative than the score alone.

0–4 minutes: Decide what needs review

A wrong answer is not the only useful signal. A skipped question may reveal a setup you did not recognize; a correct answer reached by guessing or taking too long may reveal a method you cannot yet use reliably under time pressure.

Watch three review groups in Your Mock Score Won’t Improve Until You Do This from Cracku - MBA CAT Preparation. Notice why the video examines wrong, skipped, and slow-but-correct questions. Apply that distinction only to your QA set.

For a compact logging model, read the Structure of Your Error Log and The Process of Creation subsections in Rodha’s Repeating Mistakes Without Learning. Adapt its multi-section test template to QA only. In this short revision block, aim for a useful diagnosis, not a lengthy mock-test report.

Mark each of your ten questions W (wrong), S (skipped), U (correct but uncertain), or T (correct but unusually time-consuming). A question can carry both U and T. Leave securely correct, efficient answers unmarked.

4–21 minutes: Reattempt before reading the corrections

Cover the answers and explanations below. Select up to five marked questions, prioritizing wrong and skipped ones. If fewer than five are marked, include a couple of answers you want to verify you can reproduce. If more than five are marked, choose those with a shared cause—such as repeatedly using the wrong percentage base—and put the others on your follow-up list.

For each selected question, make a fresh attempt without your old solution. Give yourself roughly three minutes per question, then use the remaining time to compare the new setup with your original work. Write one sentence beside it: “My first attempt failed at ___; the corrected starting point is ___.” If you still cannot solve it, record the first line you can justify. That makes the explanation below more useful than copying a finished solution.

21–32 minutes: Check the reasoning, not just the answer

Now compare all ten questions with the compact corrections. For each marked question, locate the first place where your reasoning departed from the correct setup. If you got a different numerical answer but used the right setup, check the arithmetic separately.

Questions 1–3: track what remains and whose score is the base. In question 1, the export stock is $80\%$ of the non-defective $85\%$, so $8840=0.80(0.85)N$. Production was $13000$, choice B. In question 2, the savings account receives $70\%$ of the half left after the fixed deposit. Thus $59500=(0.50+0.70\times 0.50)S=0.85S$, giving ₹$70000$. In question 3, express every score relative to D: $A=0.90B=0.90(1.25C)=0.90(1.25)(0.80D)=0.90D$. Since $A=72$, $D=80$.

Questions 4–5: separate categories before combining totals. In question 4, the rice-price increase accounts for $20\%$ of ₹$450$, or ₹$90$, of the ₹$150$ extra bill. Wheat accounts for ₹$60$; that is $12\%$ of its April bill, so April wheat cost ₹$500$ and May wheat cost ₹$560$, choice C. In question 5, equal metallic counts mean $0.40W=0.50B$, while $W+B=450$. Hence $W=250$ and $B=200$; $100$ of each colour are metallic. The non-metallic count is $250$.

Questions 6–8: use the stated comparison point for each change. In question 6, let $M$ be the maximum marks and $P$ the pass mark. The post-review score is $0.60M$, so $P=0.60M+35$; another $20\%$ on that post-review score gives $0.72M=P+7$. Therefore $0.12M=42$, $M=350$, and $P=245$: $70\%$, choice D. In question 7, if the first-year loss rate is $x$, then $(1-x)(1+5x)=1.35$. This gives $x=0.10$ or $x=0.70$. A $70\%$ loss would leave only ₹$3000$, contradicting “greater than ₹$5000$,” so the answer is $10\%$, choice C. In question 8, the second rate is twice the first: $(1+x)(1+2x)=1.875$. Checking $x=0.25$ gives $1.25\times 1.50=1.875$, so $25\%$, choice C.

Questions 9–10: identify the quantity to which the percentage applies. For question 9, weight equals box price divided by price per gram. The large-to-small weight ratio is $2/0.88=25/11$, so the large box weighs approximately $127\%$ more, choice A. In question 10, “$68\%$ below the pass mark” means $36$ is $32\%$ of the pass mark, not $68\%$ of the maximum. Thus $36=0.32P$, $P=112.5$, and $0.45N=112.5$, giving $N=250$, choice B.

A correction is complete when you can state why your old line was wrong. For example, “I wrote $36=0.32N$, but ‘below the pass mark’ makes $P$, not $N$, the base” is more useful than writing “Q10: B.”

32–39 minutes: Recall the methods without notes

Close the solutions and put away your earlier notes. On a blank page, write the method you would use for each of these situations, in words or a short equation:

1. A quantity changes by two successive percentage rates. How do you obtain the final value, and how would you work backward from it?
2. A stated percentage is “of the remaining amount” or “below the pass mark.” How do you identify its base?
3. A question gives total price and price per unit. How do you compare quantities bought?
4. Two algebraic answers satisfy an equation. What must you check before accepting either one?
5. You have an MCQ answer from cancellation or mental arithmetic. What quick estimate could test its plausibility?

Then uncover your notes and repair only what you could not recall. The core ideas are multipliers for successive changes; division by a multiplier to reverse a change; an explicitly named base for every percentage; quantity as total price divided by unit price; and a final check against conditions, units, and approximate size. Keep this page brief enough to revisit during later modules.

39–45 minutes: Update the weakness log

Create one row for each wrong, skipped, guessed, or unusually slow question. A notebook or spreadsheet works; use whichever you will maintain. Keep the columns specific:

Use concept gap, application/setup, arithmetic or reading slip, and time/selection as cause labels. More than one may apply, but identify the primary one. “Percentages” is too broad a difficulty label; “treated a percentage of the remainder as a percentage of the original” points to something you can repair.

Before you finish, choose one or two priority weaknesses by looking for repeated causes or costly questions. Put their question numbers on a short revisit list for roughly two days from now, then check them again during the next module’s revision. If your 45 minutes run out with some marked questions uncorrected, list those explicitly as unfinished rather than treating an answer-key glance as mastery.

You have now used the timed set for three distinct purposes: correcting faulty reasoning, testing recall, and choosing what to revisit. The recurring CAT-QA lesson is to name the base before calculating a percentage and to test every numerical result against the question’s conditions. Next, you will build on these habits in ratios, averages, mixtures, and commercial arithmetic, where identifying the right base and comparing quantities remain essential.