John has $20 to spend at a used bookstore.

He wants to buy twice as many science fiction books as mystery books.
Mystery books sell for $1.25.
Science fiction books sell for $1.75.
Tax is included in the prices.
What is the greatest number of science fiction books that John can buy?

~How would you set up this problem?

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To set up this problem, we need to determine the maximum number of science fiction books that John can buy within his budget of $20. We know that the cost of each mystery book is $1.25 and the cost of each science fiction book is $1.75.

Let's assume John buys 'x' mystery books. Since he wants to buy twice as many science fiction books as mystery books, he would buy '2x' science fiction books.

The cost of 'x' mystery books would be 1.25 * 'x', and the cost of '2x' science fiction books would be 1.75 * '2x'.

Since John's budget is $20, we can set up the following equation:

1.25 * 'x' + 1.75 * '2x' ≤ 20

Now, we can solve this inequality to find the maximum number of science fiction books John can buy.

M = S/2

1.25M + 1.75S ≤ 20

Substitute S/2 for M in the second equation and solve for S.

what is the answer