[Arithmetic. Mental arithmetic, etc.]

The tower clock strikes three times in 12 seconds. How long will it take for it to strike six times?

#
What is the interval between two adjacent strikes? Recall Problem 4.

## Solution

Since 3 strikes of the clock take 12 seconds, the interval between two consecutive strikes is 6 seconds. From the first strike to the second - 6 seconds, and from the second to the third - also 6 seconds. Six strikes, however, occur with 5 intervals. Therefore, 6 strikes will take $5 \times 6 = 30$ seconds.

## Answer

$30 \text{s}$.