Arithmetic and Numerical Ability: Standard Methods, Clean Answers
Arithmetic and Numerical Ability is the most predictable part of the MAH B.Ed CET: the same dozen topic families recur, and each has one standard method that turns a word problem into two lines of calculation.
Core topics
- Percentage, ratio and proportion, average, partnership.
- Profit and loss, discount, simple and compound interest.
- Time-work, pipes and cisterns, speed-distance-time, trains, boats.
- LCM/HCF, number system, simplification, mensuration, data interpretation.
Worked example
A finishes a task in 12 days, B in 18 days. Working together, how long do they take? Use the LCM (unitary) method rather than fractions. Take total work = LCM(12, 18) = 36 units. A does 36/12 = 3 units a day, B does 36/18 = 2 units a day, together 5 units a day. Time = 36/5 = 7.2 days, i.e. 7 days 4 hours 48 minutes. This avoids both the 1/12 + 1/18 addition and the classic error of averaging 12 and 18.
Traps that cost marks
- Chained percentage changes: a 20% rise then a 20% fall leaves 96, not 100.
- 'A is 25% more than B' versus 'B is 25% less than A': the bases differ, and the reverse figure is 20%.
- Average speed over equal distances is 2xy/(x+y), never (x+y)/2.
- For two years, CI - SI = P(r/100)^2.
- Discount applies to marked price; profit applies to cost price.