Aptitude Interview Questions

Use speed from the pole crossing, then subtract train length from total distance covered while crossing the platform.

When a train crosses a pole, it travels only its own length. When it crosses a platform, it travels train length plus platform length. If the train length is known or derivable, use speed = train length / 18 and platform length = speed * 30 - train length.

Convert percentages to multipliers and multiply them in sequence.

A 20% increase is multiplication by 1.20. A 10% decrease is multiplication by 0.90. This avoids sign mistakes and makes chained changes easier to calculate.

Cross multiply when values are positive.

For a/b and c/d, compare a*d with c*b. This avoids decimal conversion and works well in time-limited aptitude rounds.

Convert each person or machine into rate per unit time, then add rates for combined work.

If A finishes in 10 days, A does 1/10 of work per day. If B finishes in 15 days, together they do 1/10 + 1/15 = 1/6 per day, so they finish in 6 days.

Define the sample space clearly, count favorable outcomes, and check whether events are independent.

Most mistakes come from unclear event definitions. For independent events, multiply probabilities. For either/or events, add probabilities and subtract overlap when needed.