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C-DAC C-CAT study materials
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C-DAC C-CAT: Quantitative Aptitude: Arithmetic Reasoning for Section A

C-DAC C-CAT · Work through your exam, one topic at a time.

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Quantitative Aptitude: Arithmetic Reasoning for Section A

The quantitative half of Section A is arithmetic reasoning rather than formal mathematics. The recurring topics are the number system (HCF, LCM, divisibility, remainders), percentages, ratio and proportion, averages, profit and loss, simple and compound interest, time–speed–distance, time and work, pipes and cisterns, mensuration, elementary algebra, permutations and combinations, probability, and data interpretation. Speed comes from converting word problems into rates and bases, not from memorising shortcuts you cannot justify.

Working rules

  • A percentage change is measured against the base named in the question; an increase from 40 to 50 is 25%, while 50 to 40 is a 20% fall.
  • Successive percentage changes multiply. Two successive 10% rises give 1.1 × 1.1 = 1.21, i.e. 21%, not 20%.
  • Profit and loss percentages are on cost price unless stated; mark-up is on cost, discount is on marked price.
  • Average speed = total distance ÷ total time, never the plain mean of the two speeds.
  • Simple interest = PRT/100; compound interest = P[(1+R/100)^T − 1], halving R and doubling T for half-yearly compounding.
  • Keep units consistent; 1 m³ = 1000 litres, and km/h converts to m/s by multiplying by 5/18.

Worked example

A finishes a job in 12 days and B in 18 days. They work together for 4 days, then A leaves. How long does B take to finish? Take total work as LCM(12, 18) = 36 units, so A's rate is 3 units/day and B's is 2 units/day. Together they complete 5 units per day, hence 20 units in 4 days, leaving 16 units. B alone at 2 units/day needs 16 ÷ 2 = 8 more days. The LCM device keeps every rate a whole number and removes fraction errors.

Traps that cost marks

  • Adding successive discounts instead of multiplying: (1−0.1)(1−0.2) = 0.72, a 28% reduction, not 30%.
  • Using the final value as the base for a percentage change.
  • Averaging two speeds arithmetically instead of weighting by distance or time.
  • In data interpretation, ignoring a caption such as "figures in thousands" or a truncated axis.