Στρογγυλοποίηση

https://www.khanacademy.org/math/pre-algebra/decimals-pre-alg/dec-rounding-estimation-pre-alg/e/rounding_numbers


http://www.math-play.com/rounding-decimals-game-1/rounding-decimals-game.html
http://www.calculatorsoup.com/calculators/math/roundingnumbers.php

http://www.sheppardsoftware.com/mathgames/decimals/scooterQuestDecRound.htm