This is a 14-page PDF that contains a set of 24 task cards and 3 supporting worksheets that all focus on solving rate problems using a double number line diagram.
These cards are directly aligned with Common Core 6.RP.A.3b, which involves solving rate problems. Each card presents the situation and gives a partially completed double number line diagram. The rate problems range in difficulty from beginner to intermediate.
The worksheets then use a comparison of 2 different rates to determine winners in various contests. Each problem presents the situation and gives 2 partially completed double number line diagrams.
The 24 cards are 6 pages of the file (4 per card), with a 1-page recording sheet and a 1-page answer key. The worksheets are each 1-page, with 1-page answer keys, for a total of 6 pages.
When I use these, I typically print multiple sets of the task cards and have kids work in partners to go through them. To save paper, I often print the PDF in a layout that allows more than 4 cards per page. Some of the other teachers who have used the cards print them in the standard format in color and then have them laminated for centers. My students enjoy the opportunity to work at different paces and it gives me a chance to walk around and talk to different pairs of kids about what difficulties they're encountering. I would use the worksheets for either early finishers or homework.