Mathematics
Mathematics in the KS POST exam focuses on quantitative aptitude used in police and administrative work: percentages, ratio and proportion, averages, time-speed-distance, time and work, simple and compound interest, mensuration, and interpretation of tables. The aim is accuracy under a short time limit, so method choice matters as much as calculation.
Core rules
- Percentage change: always divide by the original base. A rise from 40 to 50 is (10/40)×100 = 25%, not 20%.
- Ratio: convert to a common unit before forming the ratio; scale both terms by the same factor.
- Average speed: for equal distances at speeds a and b, average speed is 2ab/(a+b), not (a+b)/2.
- Work: if A finishes in x days and B in y days, together they take xy/(x+y) days.
- Interest: simple interest = P×R×T/100; compound amount = P(1+R/100)^T.
Worked example
A sum doubles in 8 years at simple interest. What is the annual rate? Reasoning: doubling means interest earned equals the principal, so SI = P. Using SI = P×R×T/100: P = P×R×8/100 → R = 100/8 = 12.5%. The trap is to use compound-interest logic; the question specifies simple interest.
Traps
- Mixing units (metres with kilometres, minutes with hours) before applying a formula.
- Taking a percentage increase and decrease as symmetric; a 20% rise needs a 16.67% fall to return to the original.
- Using the arithmetic mean for average speed over equal distances.
- Rounding too early in multi-step problems.
Write the formula first, substitute with units, then compute.