Time & Work appears in every single SSC and RRB paper - usually 2–3 questions - and every one of them can be solved in under 45 seconds with one idea: stop working in fractions, start working in units. This is the LCM method, and this post teaches it once and then applies it to the eight patterns the exams recycle.
If A finishes a job in 12 days and B in 18 days, don't write 1/12 + 1/18. Instead let the total work be LCM(12, 18) = 36 units. Then A does 36÷12 = 3 units/day and B does 36÷18 = 2 units/day. Together: 5 units/day → 36÷5 = 7.2 days. No fractions, no LCM-of-denominators gymnastics, and every sub-question ("how much does B earn?", "what part is left?") becomes simple unit counting.
Q: A does a job in 10 days, B in 15. Together? Work = 30 units. A = 3/day, B = 2/day → 5/day → 6 days.
Q: A (12 days) and B (16 days) start together; A leaves after 3 days. Total time? Work = 48. A = 4, B = 3. First 3 days: 7×3 = 21 done, 27 left. B alone: 27÷3 = 9 days. Total 12 days.
Q: A does a job in 9 days, B in 12; they work on alternate days starting with A. Work = 36. A = 4, B = 3 → a 2-day cycle does 7 units. After 5 cycles (10 days): 35 done, 1 left. Day 11 is A's: 1÷4 = ¼ day. Answer: 10¼ days.
"A is twice as efficient as B and finishes 30 days earlier." Efficiency 2:1 means time 1:2 - the gap of one time-unit equals 30 days, so A takes 30 days, B takes 60. Together: work = 60 units; A = 2, B = 1 → 3/day → 20 days. Rule: efficiency ratio is always the inverse of time ratio.
Formula: M₁D₁H₁ ÷ W₁ = M₂D₂H₂ ÷ W₂. Q: 15 men working 8 h/day finish in 21 days. How many days for 14 men at 9 h/day? 15×21×8 = 14×D×9 → D = 2520 ÷ 126 = 20 days.
Wages divide in the ratio of work done, i.e. efficiency × days worked. A (3 units/day) and B (2 units/day) work together throughout for ₹1500 → split 3:2 → ₹900 and ₹600. If a helper C joins and they finish a 36-unit job in 6 days: A+B did 30 units, so C did 6 → C's share = 6/36 of the wage.
An outlet pipe is just negative work. Inlet fills in 6 h (tank = 12 units → +2/h), outlet empties in 12 h (−1/h). Both open: +1/h → 12 hours. The classic trap: "the leak was discovered after the tank was half full" - handle the two phases separately in units.
Q: 3 men or 5 women finish a job in 12 days. How long for 6 men and 10 women? Convert one way: 6 men = 2×(3 men) and 10 women = 2×(5 women) → total capacity = 4× the base team → 12 ÷ 4 = 3 days. Always convert everyone into one currency before adding.
(1) Adding times instead of rates - 10 days + 15 days is never 25 days together; rates add, times don't. (2) Forgetting that "leaves 2 days before completion" means the OTHER person worked those last 2 days alone - set the equation from the end. (3) In alternate-day questions, checking who works the final partial day - the exam always makes the answer differ by who starts. Drill all eight patterns in one sitting on Pareeksha's Time & Work sets - the method only becomes automatic under a timer.
The LCM (unit work) method: take the total work as the LCM of the given times, convert every person into units per day, and count units. It removes fractions entirely and answers sub-questions like wage splits directly.
In the ratio of work actually done - efficiency multiplied by days worked - never simply in the ratio of efficiencies unless everyone worked the same number of days.
Usually 2–3 questions per paper across SSC CGL/CHSL/MTS and RRB NTPC/Group D, spanning the eight standard patterns covered in this post - together, leaving midway, alternate days, efficiency ratio, MDH, wages, pipes and work equivalence.