Quantitative Aptitude / Numerical Ability
Quantitative Aptitude / Numerical Ability tests speed and accuracy across arithmetic, algebra, mensuration, and data interpretation. BHEL supervisor trainee papers typically use shop-floor contexts-production, percentage rejection, material cost, work schedules-so translate the wording into a standard equation before calculating.
Core rules and concepts
- Percentage change = (new−old)/old ×100; successive changes multiply, e.g. +20% then −10% gives 1.20×0.90=1.08, i.e. +8%.
- Ratio and proportion: keep units aligned; scale all parts by the same factor.
- Time and work: rates add; if A alone takes a days, A’s rate is 1/a per day.
- Average speed for equal distances is harmonic: 2xy/(x+y), not (x+y)/2.
- Simple interest = PRT/100; compound interest = P[(1+R/100)^T−1].
- Mensuration: circle area πr²; cylinder volume πr²h; triangle area ½bh.
Worked example
A can finish a job in 12 days and B in 18 days. Working together, their combined rate is 1/12 + 1/18 = 3/36 + 2/36 = 5/36 job per day. Time = 36/5 = 7.2 days, i.e. 7 days 4.8 hours. The reasoning is to add rates, not times; averaging 12 and 18 would wrongly give 15 days.
Traps
Adding successive percentages instead of multiplying; using simple average for speeds over equal distances; forgetting to convert minutes to hours; mixing marked price with cost price; and rounding too early in compound-interest or ratio problems. In data interpretation, check whether the question asks for percentage of total or percentage increase from a previous year.