Mathematics (Basic Arithmetic)
Mathematics (Basic Arithmetic)
Expect word problems on percentage, ratio, average, profit and loss, simple interest, LCM and HCF, fractions and speed–time–distance. There is no algebra beyond a single unknown. Marks are lost to arithmetic slips, not to hard concepts.
Rules to have at your fingertips
- BODMAS: brackets, orders, then division and multiplication left to right, then addition and subtraction left to right.
- Percentage: x per cent of N = (x ÷ 100) × N. Percentage change = (change ÷ original) × 100.
- Ratio: add the parts to get total parts, find the value of one part, then multiply.
- Average = sum ÷ count, so sum = average × count.
- Simple interest = (P × R × T) ÷ 100.
- Speed: km/h × 5/18 = m/s, and m/s × 18/5 = km/h.
- Profit and loss percentages are calculated on cost price unless the question says otherwise.
Worked example
Rs 4,200 is divided among A, B and C in the ratio 2:3:5. How much does C receive? Total parts = 2 + 3 + 5 = 10. One part = 4,200 ÷ 10 = 420. C's share = 5 × 420 = Rs 2,100. Verify: 840 + 1,260 + 2,100 = 4,200. The check takes five seconds and catches most slips.
Traps that cost marks
- Dividing by the number of people (3) instead of the number of ratio parts (10).
- Mixing kilometres per hour with metres in a train-passes-a-pole question - convert before dividing.
- Charging profit on selling price instead of cost price.
- Adding fractions by adding numerators and denominators: 1/2 + 1/3 is 5/6, not 2/5.
- Rounding midway; keep the fraction until the final line, then convert.