Tips and Ticks Combinations and Permutations


Tips and Ticks Combinations and Permutations

Permutation and combination related questions are common in PSC and Bank exams.

Before going to Combinations and Permutations, first lean about factorial.

If n is a positive integer then, factorial of n is denoted as n!.


5! = ( 1 x 2 x 3 x 4 x 5 ) = 120

4! = (1 x 2 x 3 x 4 ) = 24


Permutations are for lists of items, whose order matters and combinations are for group of items where order doesn’t matter. in other words,

  • When the order of items doesn\\\'t matter, it is called as Combination.
  • When the order of items does matter it is called as Permutation.


The number of permutations of n objects taken r at a time is determined by using this formula:

P(n,r)=n!/(n−r)!

Permutation: Listing your 3 favourite football team in order, from list of 10 teams. P(10,3) = 720.


The number of combinations of n objects taken r at a time is determined by using this formula:

C(n,r)=n!/((n−r)!r!)

Combination: Picking a team of 3 people from a football coaching group of 10. C(10,3) = 10!(3!(10−3)!) = 120.

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കോഡ്: .

മലയാളത്തിൽ \'\'കോൺവെക്സ് \" എന്നെഴുതുമ്പോൾ മറ്റ് ലെൻസുകളെ അപേക്ഷിച്ച് ദീർഘമുള്ള പേരാണ് ഇത്. അതിനാൽ ദീർഘദൃഷ്ടി പരിഹരിക്കാനുപയോഗിക്കുന്നു \' .
മലയാളത്തിലെഴുതുമ്പോൾ \"കോൺകേവ് \" എന്ന വാക്ക് മറ്റ് ലെൻസുകളുടെ പേരെഴുതുന്നതിനേക്കാൾ ചെറുതാണ്. ഹ്രസ്വദൃഷ്ടി പരിഹരിക്കാനുപ...

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Time and Work Problems - Shortcut Tricks and Formulas

Problems Type 1: .

A can finish work in X days. .

B can finish work in Y days.


Both can finish in Z days = (X*Y) / (X+Y). .


Problems Type 2: .

Both A and B together can do work in T days.

A can do this work in X days.


then, B can do it in Y days = (X*T) / (X-T) .


Problems Type 3: .

A can finish work in X days.

B can finish work in Y days.

C can finish work in Z days.


Together they can do work in T days = (X*Y*Z)/ [(X*Y)+(Y*Z)+(X*Z)] .


Problems Type 4: .

A can finish work in X days.

B can finish work in Y days.


A*X = B*Y.

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BODMAS Rule

BODMAS is an acronym and it stands for Bracket, Of, Division, Multiplication, Addition and Subtraction. .

This explains the order of operations to solve an expression. According to Bodmas rule, if an expression contains brackets ((), {}, []) we have to first solve/simplify the bracket followed by of (powers and roots etc.), then division , multiplication , addition and subtraction from left to right. .

Example :.

7 + (6 × 52 + 3) =   7 + (6 × 25 + 3).

7 + (150 + 3).

7 + (153).

7 + 153 .

Ans: 160. .

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