In a stack there are 5 books each of thickness 20 mm and 5 paper sheets each of thickness 0.016 mm.  What is the total thickness of the stack?

Thickness of one book $=20mm$

Thickness of 5 books $=5\times 20mm=100mm$

Again,

Thickness of 1 paper sheet $=0.016mm$

$\therefore$ Thickness of 5 paper sheets $=5\times 0.016mm$$=0.080m$

$\therefore$ Total thickness $=100mm+0.080mm$

$=100.08mm$

$=1.0008\times {10}^{2}mm$