[Nemo]

all three pays 300..
but the boss only takes $250

so three of them paid $250
$250/3 = $ 83.3 repeating (what each of them paid)

waiter took $20
and the three ppl got $30 back (so $10 each)

so
each paid $83.3 repeating + $10 = $93.3 repeating

$93.3 repeating x 3 people + $20 that the waiter took = $300


the logic in the ques was just misleading..

lol....then ur answer should be...
299.999999 repeating. and it is approximate to 300

u can elimite the decimal by adding 250 and 20. so the total spending will be 270. 270 + the change of 30 then it will be 300 exactly~~~lol