Quantitative Aptitude and Data Interpretation: Arithmetic Plus DI Sets
Quantitative Aptitude and Data Interpretation carries 40 questions and 50 marks in the GBO paper. Roughly half the section is arithmetic word problems, and the other half is DI sets - tabular, bar, pie, line, caselet and missing-data - where one chart feeds five questions.
Core rules
- Percentage change is always computed on the base stated: discount on marked price, profit on cost price.
- Successive change of a% and b% gives a single equivalent change of a + b + ab/100.
- Compound interest: for half-yearly compounding, halve the rate and double the time; for quarterly, quarter the rate and quadruple the time.
- Time and work: take total work as the LCM of days, convert each person to units per day, add rates.
- Speed and time are inversely proportional over a fixed distance; a 25% speed increase cuts time by 20%.
- Alligation gives the ratio of two mixtures from their deviation around the mean.
Worked example
A trader marks goods 40% above cost and allows 25% discount. Profit? Let cost = 100. Marked price = 140. Selling price = 140 × 0.75 = 105. Profit = 5 on 100, i.e. 5%. The trap is applying the discount to the cost price: 25% off 100 gives 75 and a false 25% loss.
Traps that cost marks
Confusing 'x% of' with 'x% more than'; forgetting that CI exceeds SI by the interest on interest; treating DI totals as absolute when the chart says 'in thousands'; solving approximation questions exactly and burning four minutes for one mark; and ignoring the 'quantity I vs quantity II' format, where you compare values rather than solve fully. Always read the DI axis labels and footnotes before the first question.