well it says that 60% bought so 40% did not. lets represent total people with t. s will be shirt people and n is non shirt people.
we know n = 2500 people
we also know total people equals non shirts and shirts added together. so:
t = n + s or
t = 2500 + s
we also know that n is 40% of t and that n = 2500 so
n = 40% * t or
2500 = 0.4 * t
t = 6250
we knew earlier that
t = n + s, so
6250 = 2500 + s
s = 3750
