The modal class is \(66-68\) i.e. the class (with the highest freq of 42)
Lowest class limit of the modal class \(=L_{1}=65.5\)
Upper width \(C=68.5-65.5=3\)
\(\Delta l =42-18=2: \quad \Delta_{2}=42-27=15\)
Using the formula for mode
\begin{aligned}
\text { Mode } &=L_{1}+C\left[\frac{\Delta 1}{\Delta 1+\Delta 2}\right] \\
\text { Mode } &=65.5+3\left[\frac{24}{24+15}\right] \\
&=65.5+3(0.6154) \\
\text { Mode } &=67.35
\end{aligned}