IS. 1 If all the positive factors of 28 are $d_{1}, d_{2}, \ldots, d_{n}$ and $a=\frac{1}{d_{1}}+\frac{1}{d_{2}}+\cdots+\frac{1}{d_{n}}$, find the value of $a$.
Positive factors of 28 are $1,2,4,7,14,28 \cdot a=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{7}+\frac{1}{14}+\frac{1}{28}=2$