Mathematics for BSSC CGL
The Mathematics section of BSSC CGL is arithmetic-heavy, with algebra, geometry and mensuration. Most questions test percentage, profit and loss, simple and compound interest, ratio, time and work, averages and area-volume formulas. Speed with standard shortcuts matters because the paper is time-bound.
Core rules and formulas
- Percentage: x% of N = (x ÷ 100) × N. For successive changes use a + b + ab/100, where a and b are percentage changes.
- Profit and loss: SP = CP × (1 ± gain% or loss% ÷ 100). Profit% is always calculated on cost price unless stated otherwise.
- Interest: SI = PRT ÷ 100; CI = P(1 + R/100)^T − P.
- Time and work: add rates, not days - combined rate = 1/a + 1/b; time = 1 ÷ combined rate.
- Mensuration: area of a circle = πr², triangle = ½ × base × height, volume of a cylinder = πr²h.
Worked example
A can finish a job in 12 days and B in 18 days. How long will they take together? A's one-day work = 1/12, B's = 1/18. Combined = 1/12 + 1/18 = 3/36 + 2/36 = 5/36 per day. Time = 36/5 = 7.2 days. The key step is adding work rates, not adding 12 and 18.
Traps that cost marks
- Applying the simple-interest formula to a compound-interest question.
- Forgetting to convert a percentage to a decimal before multiplying.
- Adding individual times in time-and-work problems instead of adding rates.
- Mixing units, such as centimetres and metres, inside one mensuration formula.