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permutation and combination

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Permutation and Combination permutation and combination are ways for the arrangement or selection of a group of persons/ numbers etc. Permutation is an act of rearrangement all the members of a set into same sequence or order.It is one of the different arrangement of a group of items where order / sequence / way matters whereas combination is a way of selecting members from the group such that the order of selection doesn't matter. Fundamental principle of multiplication  It there are two jobs such that one of them can be completed in m ways and second job can be completed in m ×n ways. e.g. If there are 4 ways in which a person can go from X to Y and 7 ways in which he can go from Y to Z , then possible ways to go from X to Z = 4 ×7 = 28 ways. Fundamental principle of addition If there two jobs such that they can be performed independently in m and n ways respectively , then either of the two jobs performed in (m+n) ways. Permutation By permutation we mean...
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Time And Work

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Concept of work and time         It is assumed that , if a problem does a work in n days or a pipe fills a cistern or reservoir in n days in n days , then equal amount of work on each of those days i.e. work done in a day is equal to 1/n,  Also, number of days to complete a work = 1/(work done in one day). →Efficiency is inversely proportional to the time (i.e. number of days/minutes/hours etc.). FUNDAMENTAL FORMULAE        Let M 1 men can complete W 1 work in D 1 days working H 1   h per day and earns a wages  of  ₹ R 1 Similarly , let M 2 men can complete W 2 work in D 2 days working H 2 h per days and earns a wages of ₹ R 2 Then, Efficiency problem:-     If a person A is twice as efficient as B in doing a certain work , then time taken by A is half the time taken by B to complete the work. i.e. the ratio of time taken by A and B to do the same piece of work is 1:2. ...
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