Backof The Envelope Calculations Problems
Exercises
How many movies have you seen? How many bananas have your peeled in your lifetime?
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}