The key thing to notice in doing this question is that the number we are looking for is the number of pieces of fruit on the first layer only.
To get the question right, you have to be clear about what it is asking for.
Statement 1: Of the pieces of fruit on the first layer, 6 are strawberries.
From the question we know that 25% of the pieces are strawberries.
The combination of the information from the question with the information provided in this statement is not sufficient for determining how many pieces are on the first layer. The six strawberries could be the entirety of the fruit on the first layer. The six strawberries could be all of the strawberries or a fraction of the strawberries.
Insufficient.
Statement 2: 20% of the 20 pieces of fruit on the second layer are strawberries.
This provides us with two things.
Pieces Second Layer: 20
Strawberries Second Layer: 4
However, even with the information provided in the question still don't have enough to determine how many pieces are on the first layer. Here are two possibilities.
Pieces First Layer: 20
Strawberries First Layer: 6
Pieces On Cake: 20 + 20 = 40
Strawberries On Cake: 4 + 6 = 10
Strawberries %: 10/40 = 25%
or
Pieces First Layer: 4
Strawberries First Layer: 2
Pieces On Cake: 24
Strawberries On Cake: 6
Strawberries %: 6/24 = 25%
Two different totals on first layer.
Insufficient.
Statements Combined:
Strawberries On Cake: 6 + 4 = 10
Pieces On Cake: 10/25% = 40
Pieces Second Layer: 20
Pieces First Layer: 20
Sufficient.
The correct answer is C.
