Example 1
A can finish a work in 24 days and B can finish it in 12 days. In how many days will they finish it working together?
Answer: B) 8 days
Together per day: 1/24 + 1/12 = 1/8, so time = 8 days.
Time and Work questions for competitive exams: rules, worked examples and practice
Time and work questions find how long people take to finish a job together. Work with the part of the job done per day.
Key rules and formulas
- If A finishes in a days, A does 1/a of the work per day.
- Together, A and B do 1/a + 1/b per day; time = 1 ÷ (1/a + 1/b) = ab ÷ (a + b).
- Using the LCM of the days as total work avoids fractions.
- Wages are shared in the ratio of work done.
Common traps
- Adding the days instead of the daily rates.
- Forgetting that someone left part-way through.
Where Time and Work is asked
- IBPS Clerk Prelims (Numerical Ability)
- IBPS PO Prelims (Quantitative Aptitude)
- RRB Group D (Mathematics)
- SBI Clerk Prelims (Numerical Ability)
- SBI PO Prelims (Quantitative Aptitude)
- SSC CGL Tier 1 (Quantitative Aptitude)
- SSC CGL Tier 2 (Mathematical Abilities)
Worked examples
Example 2
A can finish a work in 15 days and B can finish it in 10 days. In how many days will they finish it working together?
Answer: D) 6 days
Together per day: 1/15 + 1/10 = 1/6, so time = 6 days.
Example 3
A can finish a work in 20 days and B can finish it in 30 days. In how many days will they finish it working together?
Answer: D) 12 days
Together per day: 1/20 + 1/30 = 1/12, so time = 12 days.
Frequently asked questions
What is Time and Work in competitive exams?
Time and work questions find how long people take to finish a job together. Work with the part of the job done per day.
Which exams ask Time and Work questions?
On MockBazaar, Time and Work questions appear in IBPS Clerk Prelims, IBPS PO Prelims, RRB Group D, SBI Clerk Prelims, SBI PO Prelims, SSC CGL Tier 1, SSC CGL Tier 2.
What is the most common mistake in Time and Work?
Adding the days instead of the daily rates.