First of all i always sucked at mathematics. It was always my weakest area in school. I would argue that  0,999 in infinity is never 1 but anyways in school we usually rounded the number as long it was above +0,5 (i think or it was bit higher srrsly i dont recall well, most certantly 0,8 and 0,9 were rounded) so for example we rounded up 17,8 into 18. I dunno why they told us that way and we did it. XD