In the given figure, $DE \| BC$. Find AD.
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Given:

$DE \| BC$

To do:

We have to find $AD$.

Solution:

In $\triangle ABC$, by B.P.T., 

$\frac{AD}{DB}=\frac{AE}{EC}$

$\frac{AD}{7.2}=\frac{1.8}{5.4}$

$AD=\frac{1\times7.2}{3}$

$AD=2.4\ cm$

Therefore, $AD=2.4\ cm$.