Solution:

From the given information the modular class is 60–80.

l = 60,

The frequencies are:

fm = 61, f1 = 52, f2 = 38 and h = 20

The equation to discover the mode is

\[\begin{array}{*{35}{l}}

   Mode\text{ }=\text{ }l+\text{ }\left[ \left( fm-f1 \right)/\left( 2fm-f1-f2 \right) \right]\times h  \\

   ~  \\

\end{array}\]

Substitute the qualities in the equation, we get

\[\begin{align}

  & \begin{array}{*{35}{l}}

   Mode\text{ }=60+\left[ \left( 61-52 \right)/\left( 122-52-38 \right) \right]\times 20  \\

   ~  \\

   Mode\text{ }=\text{ }60+\left( \left( 9\text{ }x\text{ }20 \right)/32 \right)  \\

   ~  \\

   Mode\text{ }=\text{ }60+\left( 45/8 \right)\text{ }=\text{ }60+\text{ }5.625  \\

\end{array} \\

 &  \\

\end{align}\] Along these lines, modular lifetime of the parts = 65.625 hours.