Official Explanation:
The information presented can be set up in a Double-Set Matrix:
C No C Total
S 30
No S 10
Total ?
(1) INSUFFICIENT: If x represents the number of birds that are crested but not spotted, this statement yields the following:
C No C Total
S 30 x + 10 x + 40
No S x 10 x + 10
Total x + 30 x + 20 2x + 50 = ?
Without a value for x, it is not possible to find the total.
(2) INSUFFICIENT: By itself, this statement does not provide values for any unknowns in the problem.
C No C Total
S 30 > 3/5 Total
No S 10 < 2/5 Total
Total Total = ?
(1) and (2) INSUFFICIENT: The two statements together provide a filled-in matrix and a relationship between the total number of spotted birds and the total number of birds in the aviary. However, this only provides a range for the total:
C No C Total
S 30 x + 10 x + 40
No S x 10 x + 10
Total x + 30 x + 20 2x + 50 = ?
Total S > 3/5 of Total Birds
x + 40 > 3/5 (2x + 50)
x + 40 > 6x/5 + 30
10 > x/5
50 > x
If x < 50, the total number of birds, 2x + 50, must be less than 150, but this does not provide a definitive value for the total.
The correct answer is (E).