# Ex.12.2 Q4 Exponents and Powers - NCERT Maths Class 8

## Question

In a stack there are \(5\) books each of thickness \(20\, \rm{mm}\) and \(5\) paper sheets each of thickness \(0.016\,\rm{mm} \).

What is the total thickness of the stack?

## Text Solution

**What is known?**

\(5\) books of \(20\rm{mm}\) thickness each. \(5\) paper sheets of \(0.016\rm{mm}\) thickness each.

**What is unknown?**

Total thickness of the stack

**Reasoning:**

First find the total thickness of \(5\) books then find out total thickness of \(5\) paper sheets. Now find total thickness of stack by adding these two.

**Steps:**

Thickness of each book \(= 20 \,\rm{mm}\)

Number of books per stack \(= 5\)

Thickness of \(5\) books \(=5\times20=10\,\rm{mm}\)

Thickness of each sheet\(=0.016\,\rm{mm}\)

Thickness of 5 paper sheets

\(=5\times 0.016=0.080\,\,\text{mm}\)

Total thickness of stack

\[ \begin{align} &= 100 +0.080 \\ & =100.080\;\rm{mm}\\ & =100.080 \\ & =1.0008\times10^2\,\rm{mm} \end{align} \]