BODMAS Rule

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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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! . .


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:.

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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Code: ABC FIR GJ.

A : America .

B : Britain.

C : Canada.

F : France.

I : Italy.

R : Russia.

G : Germany.

J : Japan.

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