Find the value of the constant p for which 2p-1,5p+3,11are the first three terms of a linear sequence
since there is a common difference, you need
(5p+3)-(2p-1) = 11-(5p+3)
or, since the middle term is the average of the other two,
5p+3 = (2p-1+11)/2
In either case, p = 1/2