A composite bar has four sections each of length 100mm, 150mm, 200mm, and 250mm. When force is applied, all the sections causes an elongation of 0.1mm. What will be the resultant strain in the bar?

In a bar of different sections, the resultant strain is the algebraic sum of the individual stresses.

$\mathrm{Strain}=\frac{\mathrm{Extension}}{\mathrm{Length}}$

Strain in section 1 = 0.1/100
Strain in section 2 = 0.1/150
Strain In section 3 = 0.1/200
Strain in section 4 = 0.1/250
Resultant strain = 0.001+0.0006+0.0005+0.0004 = 0.00256