39. Yura borrowed a book from Lena for three days. On the first day, he read half of the book, on the second day, he read a third of the remaining pages, and on the third day, he read a number of pages equal to half the number of pages he read in the first two days. Did Yura manage to finish the book in three days?
39. On the second day, Yura read $\frac{1}{2} \cdot \frac{1}{3}=\frac{1}{6}$ of the book, so in 2 days $\frac{1}{2}+\frac{1}{6}=\frac{2}{3}$. On the third day, he read $\frac{2}{3}: 2=\frac{1}{3}$. This is exactly what he needed to read, as $1-\frac{2}{3}=\frac{1}{3}$.