Let the cost of one apple be denoted as \( a \). Then, the cost of one banana, since it is twice as expensive as an apple, will be \( 2a \).
If the person buys \( x \) apples and \( y \) bananas, the total cost can be expressed as:
\[ \text{Total Cost} = (cost , of , apples) + (cost , of , bananas) = ax + 2ay \]
We know that the person can spend at most $20, which gives us the inequality:
\[ ax + 2ay \leq 20 \]
This inequality represents the situation described. You can also factor out \( a \) (if \( a > 0 \)) to simplify it, resulting in:
\[ a(x + 2y) \leq 20 \]
However, the initial form \( ax + 2ay \leq 20 \) accurately captures the conditions of the problem, considering \( a \), \( x \), and \( y \) are all non-negative.