Positive and negative numbers

The issue of positive and negative numbers can be illustrated in various real life situations in many ways be it in hospitals and clinics, commercial situations as well as in reckoning time.

In hospitals we have got thermometers in which fine columns of mercury register the rise and fall of the human body temperature. The normal human body temperature is 37 degrees Celsius. On the thermometer the zero point indicates the position of the mercury in the tube at freezing point or the freezing point of water.

If a healthy person registers 37 degrees on the thermometer the mercury shows 37 degrees above zero. If, however, a person registers a sudden death in June it will be noticed that the temperature will abruptly fall, suppose the temperature falls 40 degrees below this point. First it falls from 37 degreees to zero, and then continues to fall for three degrtees below zero. To distinguish the degrees below zero from those above we use the plan of putting a minus sign before all those below zero and a plus sign +before those above zero.

Thus +37 means 37 degrees above zero, and -3 means 3 degrees below zero. Hence the direction up can be used to denote positive and down to indicate negative.

Similarly in commercial situations a school tuckshop owner after a certain transaction made a profit of $100. In the second deal he then made a loss of $40. Consequently in the two transactions he made a net gain of $100-$40 = $60. In the third transaction he lost $70. His profit and loss account is now shown by $60-$70. If this loss had been $60, his position would be $60-$60 = 0, that is it has reached a zero position and it is neither a loss nor gain.

But he has lost $70 not $60; therefore he has a net loss of $10, that is he is 10 below his zero.

Hence to distinguish gains from losses place negative sign before amounts showing losses and the positive sign before amounts showing profits.

In reckoning time, the numbers denoting the years are counted from birth of Christ. Years after that event are denoted by AD and those before BC. However, the use of these symbols effectively denotes the use of + and – .