(Suppose your younger brother does not know the importance of physical exercise. Now write a letter to him describing the importance of physical exercise.)
Date: 00 Month: …. Year: 0000
My Dear XYZ (Name),
I am happy to learn that you are going on well with your studies. But in the letter, there is no mention of your physical activities. You know that health is wealth. A sound mind lives in a sound body. A boy of ill health cannot reach his goal. So it needs no telling the importance of sound health to you. In order to maintain a sound mind, you are to keep your body fit at first and it is a physical exercise which enables a student to maintain a good physique. Hard work, perseverance, punctuality, sincerity, etc. are needed to cut a good figure in the examination. And this is not possible without a strong and stout body. If you fail to keep your body sound, you will lose all zest of life and then life would be dull and meaningless to you. Then you will also stumble in the way of life.
A life without a solid foundation of education is no life at all. You are told to take physical exercise regularly so that you can keep your body fit.