15. In how many ways can two letters be chosen from the word УЧЕБНИК so that one of the letters is a consonant and the other is a vowel?
15. The number of ways can be visually represented using the graph shown in Figure 94. In total, we get \(4 \cdot 3 = 12\) ways.

![](https://cdn.mathpix.com/cropped/2024_05_21_a21e90374409a05a4ea7g-83.jpg?height=463&width=1137&top_left_y=705&top_left_x=471)

Fig. 94

After solving problems 14 and 15, it is appropriate to formulate the multiplication rule for two selections.