We all know that consumer surplus is the shaded area. Mathmatically, it is integrating fromq=0 to q=Q. But the quantitiy is discrete ( q=0,1,2,3......) quantity can not be a number like 1.3, 2.5, 2.8. So I do not think consumer surplus should be calculated using integration cause some areas in which the quantity is non-positive-whole-number(like 1.3,2.5,2.8) do not exist at all. So why can we use integration to derive consumer surplus? thank you .

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