## Intermediate Algebra for College Students (7th Edition)

$\displaystyle \frac{60}{13}\approx 4.6$ hours.
In 1 hour, crew 1 dispenses $\displaystyle \frac{1}{10}$ of the needed supplies, crew 2 dispenses $\displaystyle \frac{1}{15}$ of the needed supplies, crew 3 dispenses $\displaystyle \frac{1}{20}$ of the needed supplies, In t hours , they dispense $(\displaystyle \frac{t}{10}+\frac{t}{15}+\frac{t}{20})$ of the needed supplies. We want the t (in hours) when this equals $\displaystyle \frac{1}{1}$ of the needed supplies. $\displaystyle \frac{t}{10}+\frac{t}{15}+\frac{t}{20}=1\qquad$...multiply with $LCD=60$ $6t+4t+3t=60$ $13t=60\qquad$... divide with $13$ $t$= $\displaystyle \frac{60}{13}\approx 4.6$ hours.