Bank Exam Speed Maths
Page 8: Time & Work (LCM & Efficiency Tricks)
1. Basic Concept
Work = Time × Efficiency
Example: If A completes a work in 10 days,
then 1 day work = 1/10
then 1 day work = 1/10
2. LCM Method (Fastest Trick)
Take LCM of given days as total work
Example:
A = 10 days, B = 15 days
LCM = 30 (Total work)
A's efficiency = 3 units/day
B's efficiency = 2 units/day
Together = 5 units/day
Time = 30 / 5 = 6 days
A = 10 days, B = 15 days
LCM = 30 (Total work)
A's efficiency = 3 units/day
B's efficiency = 2 units/day
Together = 5 units/day
Time = 30 / 5 = 6 days
3. Efficiency Concept
Efficiency is inversely proportional to time
Example:
A takes 10 days, B takes 5 days
Ratio of efficiency = 1:2
A takes 10 days, B takes 5 days
Ratio of efficiency = 1:2
4. Work Distribution Trick
Work is divided in ratio of efficiency
Example:
Efficiency ratio = 2:3
Work share = 2:3
Efficiency ratio = 2:3
Work share = 2:3
5. Alternate Work Concept
If A and B work on alternate days:
Calculate work done in 2 days cycle
Example:
A = 10 days → 1/10
B = 15 days → 1/15
In 2 days = 1/10 + 1/15 = 1/6
Total time = 12 days
A = 10 days → 1/10
B = 15 days → 1/15
In 2 days = 1/10 + 1/15 = 1/6
Total time = 12 days
6. Important Tricks
• Always use LCM method for faster solving
• Convert days into efficiency units
• Avoid fractions when possible
7. Practice Questions
1. A = 12 days, B = 18 days → Together time?
2. A is twice as efficient as B → ratio?
3. A = 10 days, B = 20 days → Work ratio?
4. A and B alternate days (10 & 15 days) → Total time?
5. LCM of 8 and 12 → Total work?
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