# Maths Tips and Tricks 5

## Average calculation

N = the number of terms  .

S = the sum of the numbers in the set.

Average = S/N .

For example.

The marks of a student in five subjects are 96, 94, 92, 87, and 81, then what is the average score of the student?.

N = 5.

S = 96 + 94 + 92 + 87 + 81 = 450.

A = 450/5 = 90.

Another type questions .

1). There are 36 boys and 44 girls in a class. The average score of boys is 40 and girls are 35. Then what will be the average mark? .

Total mark of 36 boys = 36 x 40 = 1440.

Total mark of 44 girls = 35 x 44 = 1540.

Total mark of 80 Students = 1440 + 1540 = 2980 .

Average mark of the class = (2980 / 80).

## Handshake Problem

Suppose there are n people in the party. The first person shakes hand with the other (n-1) guests. The second guest shakes hand with the other (n-2) guests. this will continue until the (n-1) th guest shakes hand with the nth guest.

Total number of handshakes is (n-1) + (n-2).. + 3 + 2 + 1. .

= ((n-1)(n))/2 .

For example, 6 people in a party shake hand with other guests. So how many handshakes will be there?.

=((6-1)(6))/2.

=15.

## 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. .  #### Secretariat Assistant Syllabus 2021 #### LDC Syllabus 2022 #### Tenth Level Mains Syllabus #### Secretariat Assistant Previous Question paper #### Secretariat Assistant Syllabus 2021 #### 10th level Preliminary Exam Previous Year Question Paper #### LDC Previous Question papers #### LGS Previous Question papers #### Village Field Assistant Previous Question papers #### Preliminary Exam Answer key 2021 #### Fireman Previous year Question Papers #### UPSA Previous Question papers #### LPSA Previous Question papers #### PSC Questions and Answers #### Kerala PSC Exam Calendar 