Question

how many eights are in two and a half

Answer 1

there is 20
because
16/8 = 2 
4/8 = 1/2

Answer 2

How many eights are in two and a half

This is saying how many (1/8) are in 2   1/2

This is saying how many (1/8) are in  (5/2).      Changing 2   1/2 to improper fraction.

This is solving (5/2)    ÷  (1/8)

                   = 5/2  ×  8/1   =   5 × 4 = 20

So there are 20.