## Exercises

How many hours did you spend on facebook last year?
How many golf balls will fit in this room?
About how much area would we need for a 250 car parking lot?

If the world energy consumption is about 5 x 1020 joules1 and US is about 1 x 1020 joules2, then what is the ratio of US per capita usage to that of the world as a whole?

(1)
\begin{align} USPC = \frac{1 \times 10^{20} joules} {3 \times 10^8 people} \end{align}
(2)
\begin{align} WPC = \frac{5 \times 10^{20} joules} {7 \times 10^9 people} \end{align}
(3)
\begin{align} \frac{USPC} {WPC} = \frac{\frac{1 \times 10^{20}} {3 \times 10^8}} {\frac{5 \times 10^{20}} {7 \times 10^9}} \end{align}
(4)
\begin{align} \frac{USPC} {WPC} = \frac{\frac{1 \times 10^{12}} {3}} {\frac{5 \times 10^{11}} {7}} \end{align}
(5)
\begin{align} \frac{USPC} {WPC} = \frac{1 \times 10^{12}} {3}} \times {\frac{7} {5 \times 10^{11}} \end{align}
(6)
\begin{align} \frac{USPC} {WPC} = \frac{10} {3}} \times {\frac{7} {5} = \frac{70} {15} = \frac{14} {3} \simeq 5 \end{align}