Guide
TSD appears repeatedly and CAT often embeds it inside races, trains, circular tracks or movement schedules. For CAT preparation, the useful question is not “Have I finished the chapter?” but can I recognise the version of the concept CAT hides inside a word problem and choose an efficient method under time pressure?
What to know
The core checklist for this topic is: Distance=speed×time, relative speed, average speed, trains, boats/streams, races; and circular tracks, meeting/overtaking, unit conversion. Learn these as connected ideas rather than isolated formulas. CAT often combines two of them in one question.
Recurring CAT-style forms
Expect questions built around Two objects meeting, catch-up, train crossing, equal-distance speed changes, race leads, and upstream/downstream. The wording changes, but the mathematical structure repeats. Your first 20–30 seconds should be spent identifying that structure before writing equations.
Decision rules worth remembering
- For equal distances average speed = 2ab/(a+b)
- relative speed add/subtract by direction
- convert km/h↔m/s by 5/18 and 18/5
One original example
For equal distances at 40 and 60 km/h, average speed is 2ab/(a+b)=48 km/h, not 50. The slower leg consumes more time.
The point of a worked example is not the answer; it is the choice of representation. After solving, ask whether a ratio table, base-100 assumption, sign chart, factorisation or diagram made the work shorter.
Common traps
- Taking simple mean of speeds
- wrong relative speed direction
- mixing units
- using distance ratio as time ratio without fixed speed
These traps are valuable because they explain why a student can “know the formula” and still lose marks. Add the exact mistake to your error log when it occurs; do not simply write “silly mistake.”
How to practise
Start with 10–15 untimed questions until the first step becomes automatic. Then use mixed timed sets where this topic is not announced in advance. Finish with sectionals and mock review. Mastery checkpoint: Can draw a timeline/route diagram and solve meeting/catch-up problems without excessive variables.
Once that checkpoint is stable, move on rather than over-polishing one chapter. CAT QA is a portfolio of scoring areas; the objective is enough reliable topics to make question selection easy on exam day.
Preparing for CAT?
See where you actually stand before changing your shortlist or study plan.
Why On Your Mocks?
A mock score tells you what happened. OYM helps you understand what went wrong and what to work on next.