# Kerala PSC Maths Tips and Tricks 3

## Simple and Compound Interest Formula

P - Principal, the sum of money lent or borrowed. .

R - Rate of interest: Annual interest, often expressed as a percentage. .

T - Time period for which the money is lent or borrowed. .

Simple Interest = Principal * Time * Rate of interest / 100 .

SI = 4000× 8% × 4 =  4000× 0.08 × 4.

= 1280. .

In compound interest , the principal amount with interest after the first time period becomes the part of principal for the next time period.

CI =   [P (1 + R/100)^T] – P .

Total amount = [P (1 + R/100)^T] .

If time period is half-yearly, .

Amount = P[1 + (R/2)/100]^2T .

If time period is quarterly, .

Amount = P[1 + (R/4)/100

## 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! . .

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. .

## ഗണിത സൂത്രവാക്യം

ആദ്യത്തെ \'n\' എണ്ണൽ സംഖ്യകളുടെ തുക = n(n+1) /2.
ആദ്യത്തെ \'n\' ഒറ്റ സംഖ്യകളുടെ തുക = n².
ആദ്യത്തെ \'n\' ഇരട്ട സംഖ്യകളുടെ തുക = n(n+1).
ആദ്യത്തെ \'n\' എണ്ണൽ സംഖ്യകളുടെ വർഗ്ഗങ്ങളുടെ തുക = n(n+1)(2n+1) / 6.
ആദ്യത്തെ \'n\' എണ്ണൽ സംഖ്യകളുടെ ക്യൂബുകളുടെ തുക = [n(n+1)/ 2]².
ആദ്യ പദം \'a\', പൊതു വ്യത്യാസം \'d\' ആയാൽ n-മത്തെ പദം കാണാൻ = a+ (n -1) d.
ആദ്യ പദം \'a\', പൊതു വ്യത്യാസം \'d\' ആയാൽ, n പദങ്ങളുടെ തുക കാണാൻ = n/2[2a + (n - 1)d].
ആദ്യ പദവും (t1), n

## 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. .