Question

A series of ocean waves are moving past a surfer at a frequency of 25 waves per hour. approximately how many waves should the surfer expect during 45 minutes?

Answer 1

45 minutes corresponds to $\frac{3}{4}$ of hour. There are 25 waves per hour, so we must find how many waves there are in $\frac{3}{4}$ of hour. Therefore we can write the following proportion:
$25 waves: 1h = x : \frac{3}{4} h$
and by solving ,we find
$x= \frac{25 \cdot \frac{3}{4} }{1 }=18.75 waves$
So, the surfer should expect almost 19 waves in 45 minutes.