Question

A park ranger calculated that 60% of the deer they tagged were male. Of the male deer that were tagged, 20% of them were older than 4 1/2 years. They tagged 18 male deer that were older than 4 1/2 years. How many deer did they tag?

Answer 1

$$
\large{
0.6D=M\\
0.2M=18\\\\
M=\cfrac{18}{0.2}\\
D=\cfrac{M}{0.6}
}
$$

That's it!

Make sense?