Question

In a stack there are 10 books each of thickness 10 mm and 8 paper sheets each of thickness 0.015 mm. What is the total thickness of the stack?

• A. $112mm$
• B. $1.12\times {10}^{2}mm$
• C. $1.012\times {10}^{2}mm$
• D. $1.0012\times {10}^{2}mm$

Answer 1

The correct option is D $1.0012\times {10}^{2}mm$

$\text{Thickness of one book}=10\text{mm}$
$\therefore \text{Thickness of 10 books}=10\times 10\text{mm}=100\text{mm}$

$\text{Thickness of one paper sheet}=0.015\text{mm}$
$\therefore \text{Thickness of 8 paper sheets}=8\times 0.015\text{mm}=0.12\text{mm}$

$\text{Total thickness of the stack}=(100+0.12)\text{mm}=100.12\text{mm}$

$100.12=\frac{10012}{100}=\frac{1.0012\times {10}^4}{{10}^2}$
$=1.0012\times {10}^2(\because \frac{a^m}{a^n}=a^{m-n})$
Thus, the thickness of the stack is $1.0012\times {10}^2\text{mm}.$