Question

In $8$ days, the earth picks up $(6.4\times {10}^7)kg$ of dust from the atmosphere. How much dust will it pick up in $15$ days?

Answer 1

Let $xkg$ dust will be picked up in $15$ days.

$\begin{array}{ccc}\text{Time in days}& 8& 15\\ \text{Dust pick up in kg}& 6.4\times {10}^7& x\end{array}$

(more time, more dust, i.e. directly proportional relation)

$\therefore \frac{8}{6.4\times {10}^7}=\frac{15}{x}$

$\Rightarrow x=\frac{6.4\times {10}^7\times 15}{8}$

$\Rightarrow x=12\times {10}^7=1.2\times 10\times {10}^7=1.2\times {10}^{8}kg$