United Nations Assembly
Time & Work – LCM, Efficiency & Shortcut Tricks
Time and Work is a key topic in bank exams. Use LCM and efficiency methods to solve quickly.
1. Basic Concept
Work ∝ Efficiency
More efficiency → Less time
Formula:
Work = Time × Efficiency
2. LCM Method (Most Important)
Example:
A can do work in 10 days
B can do work in 15 days
Solution:
LCM = 30 units
A = 3 units/day
B = 2 units/day
Total = 5 units/day
Time = 30 ÷ 5 = 6 days
3. Efficiency Concept
Efficiency is inversely proportional to time
Example:
A takes 10 days, B takes 20 days
Ratio of efficiency = 2 : 1
4. Work Together Formula
Formula:
(A × B) ÷ (A + B)
Example:
A = 10 days, B = 20 days
= (10×20)/(10+20) = 200/30 = 20/3 days
Tough Problems
Q1:
A can do work in 12 days, B in 18 days. Find time together.
Solution:
LCM = 36
A = 3 units/day
B = 2 units/day
Total = 5 units/day
Time = 36 ÷ 5 = 7.2 days
Q2:
A does half work in 5 days. How much time for full work?
Solution:
Half work = 5 days
Full work = 10 days
Q3:
A and B together complete work in 6 days. A alone takes 10 days. Find B alone.
Solution:
(A+B) = 1/6
A = 1/10
B = (1/6 - 1/10) = (5-3)/30 = 2/30 = 1/15
B = 15 days
Exam Strategy
- Always use LCM method for speed
- Convert days into efficiency
- Avoid direct calculations
- Practice combined work questions
Quantitative Aptitude • Bank Exams • Competitive Preparation
Focused Study for Competitive Exams
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