The rate of his grade point average G is \(\frac{dG}{dt}\) and the word "increasing ” indicates that the constant k will be positive . Also, \(\displaystyle{\frac{{{d}{G}}}{{{\left.{d}{t}\right.}}}}\) is directly proportional to N and inversely proportional to A indicates that N will be the numerator and A the denominator.

\(\frac{dG}{dt}=\frac{kN}{A},(k>0)\)