Mathematics
Mathematics is the largest section of AISSEE: 50 questions worth 3 marks each (150 marks), with one-third negative marking for a wrong answer. It tests numerical accuracy across the number system, HCF/LCM, fractions and decimals, ratio and proportion, percentage, profit and loss, simple interest, average, speed, mensuration and basic geometry; Class IX adds algebra, polynomials, linear equations and surface areas/volumes. Because each question is worth 3 marks, one careless unit slip can cost more than a reasoning question.
Core rules to keep ready
- Follow BODMAS: brackets, orders, division/multiplication left to right, then addition/subtraction.
- Convert before comparing: 0.4 = 40% = 2/5; 1 m = 100 cm, 1 m² = 10,000 cm².
- Ratio share = total × (own ratio)/(sum of ratios).
- Rectangle: A = l×b, P = 2(l+b); triangle: A = ½×b×h; circle: C = 2πr, A = πr²; cuboid: V = lbh, total surface area = 2(lb+bh+hl).
- Percentage change uses the original quantity as denominator; successive changes multiply factors.
Worked example
A shop marks an article at ₹800 and allows 15% discount, yet gains 20%. Find the cost price. Selling price = 800 × (1 − 0.15) = 800 × 0.85 = ₹680. Gain of 20% means SP = 1.20 × CP, so CP = 680 ÷ 1.20 = ₹566.67 (₹1700/3). Check: 20% of 566.67 ≈ 113.33; 566.67 + 113.33 = 680. The common error is taking 15% of cost price instead of marked price.
Traps that cost marks
Mixing perimeter and area; forgetting to convert cm to m before multiplying; using the selling price as the base for a profit percentage; and guessing under negative marking. Eliminate two options first, and skip a question when no option can be ruled out.