Question: You are gleaning a report and see that recent U.S. GDP is $16,535 billion and recent U.S. exports are $2195.9 billion. You don’t have a calculator and don’t want to divide.
Approximate U.S. exports as a percent of U.S. GDP.
Approximation: Note that 10% of GDP is $1,653 billion. Since exports are $2,195 billion the answer is a bit above 10%.
How much above 10%?
Note that 1.0% of GDP is $165 billion.
($2195-1,653) is a bit over 500. 165 goes into 500 a bit more than 3 times.
I get around 13%, maybe a bit more.
It is useful to be able to get quick approximations.
Hope this is helpful.
It may have been easier to divide each number by 1000. Change $2195 to $2.2 and $16,535 to $16.5. Take 10% of $16.5 and get 1.65. (Note that (2.2-1.65) is around 5.7. I am closer to 13.5 this time.