Formula

A formula is formed by using:A formula is formed by using:

(a) mathematical symbols and variables

(b) given conditions, and

(c) simplification.

Some well known formulae are listed below:

Area of a rectangle A = l x b

A = Area

l = Length

b = Breadth

Perimeter of a rectangle P = 2(l + b)

P = Perimeter

Volume of a cuboid V = l x b x h

V = Volume

h = height

Simple interest

P = Principal

T = Time

R = Rate percent per annum

In an n-sided polygon, the number of diagonals d, which can be drawn from one vertex, is 3 less than the number of sides of the polygon. Write this as a formula. Express d in terms of n.

Number of diagonals = d

Number of sides of a polygon = n

the required formula is = d = n -3

The sum of the reciprocal of x and the reciprocal of y equals the reciprocal of m. Express this as a formula.

Reciprocal of

Reciprocal of

Reciprocal of

The required formula is

The average weight of each of 'p' boys and 'q' girls is x kg and y kg respectively. Frame a formula for the average weight of (p + q) students.

Average weight of each of 'p' boys = x kg

Their total weight = px kg

Average weight of each of 'q' girls = y kg

Their total weight = qy kg

Total weight of [p + q] students = [px + qy] kg

Average weight of [p + q] students

A number of two digits p and q in that order is 7 greater than the number formed by reversing the digits.

The ten's digit is p and the unit's digit is q.

Then the number is 10p + q.

The number formed by reversing the digits = 10q + p

(10p + q) - (10q + p) = 7

A man walks for 'a' hours at x km/hr and then cycles a distance of 'b' kilometres at y km/hr. Write down an expression for his average speed in km/hr for the whole journey.

Distance Time Speed

(1) ? a x

(2) b ? y

In the first case, the man walks at x km/hr for 'a' hours, so he covers a distance of (xa) kilometres. In the second case, he cycles for 'b' kilometres at a speed of y km/hr, so he takes (b/y) hours.

the total distance he covers = (xa + b) and

the total time he takes

Average speed