Formulae
Rule - 1: Equal numbers may be added to (or subtracted from) both sides of an equation.
Rule - 2: Both sides of an equation may be multiplied (or divided) by the same non-zero number.
Rule - 1: Equal numbers may be added to (or subtracted from) both sides of an inequality without affecting the sign of inequality.
Rule - 2: Both sides of an inequality can be multiplied (or divided) by the same positive number. But when both sides are multiplied or divided by a negative number, then the sign of inequality is reversed.