Have to calculate

one night ,communltd, 3 people go to a hotel , 300 yuan a night . Cut each of the three is just 300 yuan to 100 yuan lobbied for a boss. 3 × 100 = 300 ( yuan ) -

boss said later today in town, offers to 250 yuan, 50 yuan out of the waiter returned to command the three of them . -

300-250 = 50 ( million ) -

secretly hid the waiter 20 yuan , 30 yuan for the remaining points to the three of them , each assigned to 10 yuan . -

50-20 = 30 ( million ) -

30 ÷ 3 = 10 ( million ) -

way, just dig a 100 yuan per person , now back 10 yuan , which is 90. -

100-10 = 90 ( million ) -

spent only 90 yuan per person , 3 people is 90 yuan per 270 yuan -

3 × 90 = 270 ( yuan ) -

plus waiter is unseen from 20 per 290 , -

270 +20 = 290 ( yuan ) -

and 10 dollars gone? ? ? -

300-290 = 10 ( million ) -

-

Who can tell me where it went to 10 dollars in the end ah ?