This is a very engaging math center for your students. You will need to download a free app called Population Matters. Included is two, two page center worksheets. They focus on the following skills: expanded notation, word form, scientific notation, rounding, ordering from greatest to least, comparing by subtracting differences & predicting. I give two days for each 2 page worksheet. So, in all, four days worth of engaging population center ideas. :) Enjoy. Check out my other math centers too.