CDS Mathematics · Teaching notes
Time and Work — CDS Elementary Mathematics
Time and Work has 46 past-year questions in CDS Elementary Mathematics, in 18 of the twenty-one sittings from 2016 (II) to 2026 (II). Man-days alone account for 17 of them, and only three are HARD: work with rates, which add, and man-days, which stay fixed for a job, never with days directly. The pages go from work rates to man-days, then to gangs of men and women, and end with pipes and cisterns.
Every subtopic, worked example, formula and trap in one printable document — answers shown, ready to share.
Subtopic notes
Work Rates
14 PYQsSomeone who finishes a job in n days does 1/n of it each day; rates add when people work together.
Man-Days and Man-Hours
17 PYQsA fixed job needs a fixed number of man-days (or man-hours), so men × days × hours stays constant for the same work.
Men, Women and Equivalent Workers
9 PYQsWhen a gang mixes kinds of worker, first find each kind's daily rate (or how many of one equal one of the other), then add the gang's rates.
Pipes and Cisterns
6 PYQsPipes are workers whose job is filling a tank; an outlet is a worker with a negative rate.
Formula & revision sheet
5 formulas · 7 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
5 formulas · 7 gotchas across all subtopics — the exam-eve cheat-sheet
Watch out for (3)
- Times do not add→ Adding and subtracting rates
- Pay by rate, not by time→ Adding and subtracting rates
- The last turn may be partial→ Joining, leaving and taking turns
Formulas (1)
Watch out for (2)
- Count the whole job, not the part→ Men × days × hours
- Additional men, or men in all?→ Men × days × hours
Formulas (1)
Watch out for (1)
- OR is not AND→ Rates of different workers
PYQ weightage by concept
5 concepts · 46 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
5 concepts · 46 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Adding and subtracting rates | 10 | 22% |
| Joining, leaving and taking turns | 4 | 9% |
Test yourself on Time and Work
15 past CDS questions from this chapter, timed at 18 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.