If there are12 books on a rack,a person has to choose 5books. In how many ways can he choose if one particular book is always selected?​

330

11 choose 4

Step-by-step explanation:

Here is the solution.
Let s = small cups and l = large cups
s + l = 155
1.25s + 2.50l = 265
s = 155 - l
(now substitute)
1.25(155-l) + 2.50l = 265
193.75 - 1.25l + 2.50l = 265
1.25l = 71.25 (divide both sides by 1.25)
l = 57
Therefore there are 57 large cups sold
Next, 
s + 57 = 155
s = 98
There are 98 small cups sold.
Hope this answers your question.