Exercise 47 Page 264

To determine how many pencils we need, we should divide the distance from the earth to the moon by the average length of the pencil.

\frac{3 . 8 4 4 \times 1 0 ^{8}}{1 . 8 \times 1 0 ^{- 1}}

Write as a product of fractions

\frac{3 . 8 4 4}{1 . 8} \times \frac{1 0 ^{8}}{1 0 ^{- 1}}

$a^{- 1} = \frac{1}{a}$

\frac{3 . 8 4 4}{1 . 8} \times \frac{1 0 ^{8}}{1 / 1 0}

$\frac{a}{b / c} = \frac{a \cdot c}{b}$

\frac{3 . 8 4 4}{1 . 8} \times \frac{1 0 ^{9}}{1}

Calculate quotient

2.13555 \dots \times 1 0^{9}

Round to $3$ decimal place(s)

\approx 2.135 \times 1 0^{9}

We need about

2.135 \times 1 0^{9}

pencils.