A bakery sells three sizes of cakes: small, medium, and large. The size of the cakes and their respective prices are as follows:
Small cake: $\frac{2}{5}$ of a whole cake, priced at $10.
Medium cake: $\frac{3}{5}$ of a whole cake, priced at $15.
Large cake: whole cake, priced at $25.
Each size of cake is made from the same ingredients, but the proportions vary by size. If a customer buys:
What fraction of a whole cake does the customer effectively purchase in total?