What is 15 - 20?

The expression 15 - 20 involves taking 20 away from 15, which can be visualized on a number line as starting at 15 and moving left by 20 units. Moving left by 15 units from 15 reaches zero, then another 5 units left results in -5. Hence, 15 - 20 equals -5. This solution uses the basic rule that subtracting a larger number from a smaller one will yield a negative result, in this case, moving leftward to achieve -5 as the answer.