Question

Find the third proportional to
$36,18$

Answer 1

Let the third proportional to $36,18$ be $x$
Then $36,18$ and $x$ are in continued proportion
$36:18::18:x$
Using the cross product the rule
Product of extremes =Product of means
$36\times x=18\times 18$
$x=9$
Hence, the third proportion is $9$