Question

The shadow of a 3m long stick is 4m long. At the same time of the day, if the shadow of a flagstaff is 24 long, how tall is the flagstaff?

Answer 1

Let the length of flagstaff is $x$.
Shadow : Length :: Shadow : Length
$4m:3m::24m:x$
$\frac{4}{3}=\frac{24}{x}$ [ if, a,b,c and d are in proportion, then $\frac{a}{b}=\frac{c}{d}$]
$4\times x=3\times 24$
$x=\frac{3\times 24}{4}$ [by cross multiplication]
$x$ = 18
Hence, the flagstaff is 18 m tall.