A tree is 12 m tall and casts an 8 m long shadow. At the same time, a flag pole casts a 100 m long shadow. How long is the flag pole:

It is given that the original height of 8m casts a shadow $= 12 \mathrm{m}$

Therefore, we can say that 1m of height would cast a shadow  $=\frac{12}{8}$

Now, to find the shadow casted by a height of 100 m 

$=\frac{12}{8}\times 100$ 

$=\frac{2\times 6}{4\times 2}\times 4\times 25$

$=\frac{\cancel{2}\times 6}{\cancel{4}\times \cancel{2}}\times \cancel{4}\times 25$

$= 6 \times 25$

$= 150 \mathrm{m}$