It takes 4 carpenters 4 minutes to nail 4 boards in place. At this rate, how long will it take 80 carpenters to nail 80 boards in place?

Answer 1

1 carpenter nails n boards / minute
so
4 carpenters ( n boards/ carpenter min) ( 4 min) = 4 boards
n = 1/4 boards / carpenter min
80 carpenters ( 1/4 boards/ carp min) (t min) = 80 boards
80 t = 80*4
t = 4 minutes