Four people can mow a lawn in 6 hours. How many more people will be needed to mow the lawn in 4 hours, assuming each person mows at the same rate?
The number of people mowing and the time required to mow are inversely proportional. Letting $n$ be the number of people and $t$ be the amount of time, we have $nt = (4)(6)= 24$ because 4 people can mow a lawn in 6 hours. If $m$ people can mow the lawn in 4 hours, then we must have $m(4) = 24$, so $m=6$.  Therefore, we need $6-4 = \boxed{2}$ more people to complete the job in 4 hours.