17. For conducting research on a certain field, a random sample of 200 wheat ears was taken. The relative frequency (frequency) of ears having 12 spikelets per ear turned out to be 0.125, and for 18 spikelets it was 0.05. Find the frequencies of ears having 12 and 18 spikelets in this sample.
S o l u t i o n. Let's consider the events: $A$ - a spike with 12 spikelets is taken; $B$ - a spike with 18 spikelets is taken.

Let's find the frequencies $m_{1}$ and $m_{2}$ of events $A$ and $B$, using formula (5).

Denote by $W_{1}(A)=\frac{m_{1}}{n}$ the relative frequency of event $A$, and by $W_{2}(B)=\frac{m_{2}}{n}$ the relative frequency of event $B$. Since the number of trials conducted is $n=200$, then $m_{1}=W_{1}(A) \cdot n=0.125 \cdot 200=25$, $m_{2}=W_{2}(B) \cdot n=0.05 \cdot 200=10$.