Elementary Mathematics
Elementary Mathematics
This domain checks numerical fluency up to class 10 level: number system, percentage, ratio, average, interest, time-speed-distance, time-work, mensuration and basic algebra. Accuracy depends on choosing the right base and unit.
Core rules
- Percentage change: successive changes of a% and b% give a+b+ab/100.
- Interest: SI = PRT/100; CI = P(1+r/100)^n − P.
- Average speed: total distance ÷ total time, not the mean of speeds unless distances are equal.
- Work: add rates; if A does 1/12 and B 1/18 per day, together they do 5/36 per day.
- Ratio: convert all quantities to the same unit before forming the ratio.
- Mensuration: area of circle = πr²; triangle = ½bh; volume of cylinder = πr²h.
Worked example
A trader marks an article 25% above cost and allows a 10% discount. Let cost = 100. Marked price = 125. Selling price = 90% of 125 = 112.50. Profit = 12.50 on 100, so profit = 12.5%. The discount is on the marked price, not the cost.
Traps
Applying SI formula to CI; using arithmetic mean for average speed; taking discount on cost price; forgetting 5/18 to convert km/h to m/s; mixing simple and compound interest periods; counting inclusive days or fenceposts incorrectly; using the wrong base in percentage questions.