# At their annual car wash, the science club washes 30 cars in 45 minutes. At this rate, how many cars will they wash in 1 hour?

$\text{40 cars/hour}$
$\text{30 cars"/"45 minutes" = "10 cars"/"15 minutes}$ (simplified).
Now, since there's $60$ minutes in an hour, multiply $15$ by $4$, and do the same thing to the other side. That's $40$ cars in $60$ minutes, or $\text{40 cars/hour}$