https://www.transum.org/software/SW/Starter_of_the_day/Students/Rounding.asp
https://www.khanacademy.org/math/arithmetic-home/arith-review-decimals/arithmetic-significant-figures-tutorial/e/significant_figures_1
Significant Figures Grid Game
https://quizizz.com/admin/quiz/59bfe431d8eb9411003e0e62/significant-figures-practice