Achemist is mixing a 40% salt solution with a 20% salt solution to make 50 l of
a new solution that will contain 25% salt. how much of each of the original
solutions should the chemist use?

Let be the amount (in L) of the 40% solution to be used, and the amount (L) of the 20% solution. The chemist wants a new solution of 50 L, so that

Each L of the 40% solution contributes 0.4 L of salt, while each L of the 20% solution contributes 0.2. The new solution should have a concentration of 25% salt, so that

Now

to find the total number of combinations, multiply the quantity of each item by each other:

2 pairs of shoes x 3 pairs of shorts = 6 different combinations.