General Aptitude
General Aptitude in GATE PH tests numerical ability, logical reasoning, data interpretation, and verbal ability. The section is scoring because the mathematics is elementary, but the wording is designed to punish rushed reading and unit slips.
Core rules and concepts
- Percentage change uses a base. A successive increase and decrease of the same percentage does not cancel: multiply the factors.
- Ratio and proportion problems are safest when converted to a common unit before forming equations.
- Data interpretation requires reading axis labels, units, and the year or category being compared. Compute only the values needed for the options.
- Logical reasoning includes syllogisms, seating arrangement, number series, and coding-decoding. In syllogisms, draw minimal Venn diagrams and test whether the conclusion is forced.
- Verbal ability tests grammar, vocabulary in context, and sentence completion; the correct option must fit both meaning and syntax.
Worked example
A quantity is increased by 20% and then decreased by 20%. After the increase it becomes 1.20 times the original. After the decrease it becomes 0.80 × 1.20 = 0.96 times the original. The net change is a 4% decrease, not zero. The common error is to add +20% and -20% and conclude no change.
Traps that cost marks
- Adding successive percentages instead of multiplying factors.
- Mixing units such as rupees and paise, or km/h and m/s.
- Selecting a conclusion that is possible but not logically forced.
- Reading a graph's trend without checking the axis scale.