91Ó°ÊÓ

In mathematics, a variable (usually an English alphabet) standing for an unknown value in any equation or Algebraic Expression. In general we used x, y, z or t (time) , d (distance) and r for radius.

Algebraic expressions include at least one variable and at least one operation (addition, subtraction, multiplication, division).

For example, 7(6y + 9z) is an algebraic expression.

Rules of Multiplication of Integers

RULE 1: The product of a positive integer and a negative integer is negative.

RULE 2: The product of two positive integers is positive.

RULE 3: The product of two negative integers is positive.

Rule:The product of two positive integers is positive.

Consider, the expression provided in the question: $20  ·  5  +  7  ·  3 $

To determine the value of $20·5+7·3$, at first 20 is to be multiplied by 5 and 7 is to be multiplied by 3. After this step the result of both the multiplication is to be added.

The expression will be obtained as:

$\begin{array}{l}20â‹\dots 5+7â‹\dots 3\left[\text{Multiply}\right]\\ 100+21=121\left[\text{Add}\right]\end{array}$

The value of the expression $20  ·  5  +  7  ·  3 $is 121.