Divisibility 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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What is the divisibility by 2 Rule?.
Even numbers are multiples of 2. A number is even if ends in 0,2,4,6, or 8.
What is the divisibility by 3 rule?.
A number is divisible by 3 if the sum of its digits is divisible by 3.
372, for instance, is divisible by 3 since sum of its digits (3+7+2) is 12. And 12 is divisible by 3.
What is the divisibility by 4 rule?.
A number is divisible by 4 if the number\'s  last two digits are divisible by 4.
9,312, for instance, is divisible by 4 since its last 2 digits are 12. And 12 is divisible by 4.
What is the divisibility by 5 rule?.
A number is divisible by 5 if its last digit is a 0 or 5.
What is the divisibility by 6 rule?.
Since 6 is a multiple of 2 and 3, the rules for divisibility by 6 are a combination of the rule for 2 and the rule for   3.
Divisibility by 8 Rule.
A number passes the test for 8 if the las...

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