5. Which of the fractions is greater: $\frac{199719973}{199719977}$ or $\frac{199819983}{199819987}$?
5. We will compare not the numbers themselves, but their complements to 1. $\frac{4}{199819987}<\frac{4}{199719977}$, from which: $\frac{199719973}{199719977}<\frac{199819983}{199819987}$.