5. Four friends (from 6th grade, 1 point). Masha, Nina, Lena, and Olya are friends. They are all of different heights, but the difference is very small - it's hard to tell by eye. One day they decided to find out who is taller and who is shorter. It turned out that Nina is shorter than Masha, and Lena is taller than Olya. What is the probability that Nina is taller than Lena under these conditions?
Solution. The following equally possible distributions by height in descending order are possible:

## MNLO, MLNO, MLOL, LOMN, LMON, and LMNO.

Out of these six elementary outcomes, only one - MNLO - is favorable to the event "Nina is taller than Lena."

Answer: $1 / 6$.