Answer:
The wedding planner must have purchased 28 small lanterns and 12 large lanterns.
Explanation:
Let the number of small and large lanterns purchased be S and L respectively.
S + L = 40 ........ Equation 1
L = 40 - S
25S + 40L = 1180 ....... Equation 2
25S + 40(40 - S) = 1180
25S + 1600 - 40S = 1180
-15S = 1180 - 1600
-15S = -420
S = 28
L = 40 - S
L = 40 - 28
L = 12
The wedding planner must have purchased 28 small lanterns and 12 large lanterns.