3b. Solve unit rate problems including those involving unit pricing and constant speed. For example, if it took 7 hours to mow 4 lawns, then at that rate, how many lawns could be mowed in 35 hours? At what rate were lawns being mowed?

In our happy diaper situation from before (35 diapers in 7 days), the simplest form of the ratio also happens to be the unit rate as described by the second part of the standard. Once we solve for the unit rate (5 diapers per day), we multiply to solve for any future event because the relationship is consistent. For example, we could whip out a little multiplication along with that unit rate to find that we use 140 diapers in 28 days. Yikes.

This concept is also a big deal when we talk about unit pricing. If diapers cost $20 for a pack of 100, their unit price is $0.20 per diaper. And we can use that to figure out how much we'll need to spend on those 140 diapers.