Question

2 Fermi Problems?

1) How many gallons of gasoline are used by cars each year in the country you live in?

2) In the 1989 Loma Prieta earthquake in California, approximately 2 million books fell off the shelves at the Stanford University library. If you were the library administrator and wanted to hire enough part-time student labor to put the books back on the shelves in order in 2 weeks, how many students would you have to hire? (You may assume that the books just fell off the shelves and got a bit mixed up but books in different aisles did NOT get shuffled together.)

**thank you:)

Answer 1

@MrNood do you get these?

Answer 2

As before - it is about making 'reasonable asumptions'

How many people live in your country?
What % of them own a car?
What is the average mileage driven by each owner?
What is th eaverage consumption per mile of each car

These estimates will lead oyu to an estimate for the answer
But be aware the % uncertainty in the answer is the SUM of the % uncertainties in all your assumptions.

2nd one:

How many books can 1 student handle per hour?
How many hours are available (2 weeks - is this 60, 70 80 hours?....)
How many stubdents are therefore required...

There is no 'CORRECT ' answer , but you should justify your assumptions and minimise the potential errors where possible.

Answer 3

okay:) #1: so the country is the US and the population is over 7 billion

and i believe 90% of americans use cars; average mileage is 12,000 a year
not sure about average consumption though?

and for #2, a student can handle about 50 books an hour? And hours available are 5 hours a week?

how would that be calculated?

Answer 4

oh about 10 cents per mile!

Answer 5

for the consumption:)

Answer 6

@MrNood ?

Answer 7

how would i put it together into a calculation?

Answer 8

You can do all these sums - it is simple arithmetic
The population aof US is NOT 7 billion +
you are looking for miles per gallon, not cents/mile

and why only 5 hours per week - real people (not students ( :-) work 30-50 hours per week.

Answer 9

oops sorry 316 million!

Answer 10

ohh okay:) then 40 hours a week?

Answer 11

not sure what miles per gallon are? like 15 miles per gallon?

Answer 12

how do i add them up?

just all values added up? even the percentages?? @MrNood

Answer 13

as an example

100 million population
20% own a car ( i.e. 1 car for every 5 people)

means 20 million cars

average mileage 10000 miles per year means
total 200,000 million miles per year are driven

average consumption 40 miles /gallon
50 billion gallons of fuel
JUST an example - put you OWN estimates in

NO- you generally multiply them

Answer 14

oh ok! so would i do this?

316 million population with 9 cars for every 10 people = 284,400,000 million cars?

average mileage is 12000 with a total of 2,844,000,000 billion miles?

average consumption is 50 miles per gallon so 56880000 billion gallons of fuel? @MrNood

Answer 15

and for the second one, do i do this?

50 books per hour; 40 hours a week

so 50*40=2000 books

and then 2000000 books divided by 2000=1000 students must be hired?

Answer 16

oh i looked it up, and it says 90% of americans own a car...

Answer 17

OH come ON - just take a look at YOUR figures - are they reasonable
Are there that many cars?

I am not going to do this for you

it is about REASONABLE that is SENSIBLE estimates and simple maths.

You have not made reasonable estimate (9/10 people do NOT own a car - many are old/young/disadvantaged)
and even if they did - you can quickly see that your figures are ridiculous - you have far more cars than people yet you estimated that not all people have a car!

Take a deep breath, take some time and do some sensible maths

Answer 18

Well that is not true - 909% of Americans are not of the right age to own a car for starters.

Your second answer is better - but I would not be happy to employ someone who only handled 1 book per minute

Answer 19

ahh okay, sounds good. thank you very much!