Final answer:
An addition expression where the addends have opposite signs and the sum is -3 1/4 can be -6 1/2 + 3 1/4. The larger number in absolute value is negative, thus leading to a negative sum.
Step-by-step explanation:
To write an addition expression where the addends have opposite signs and the sum is -3 1/4, we can select one positive and one negative number that when combined equal -3 1/4. Let's use -6 1/2 and 3 1/4 as an example.
Following the rule that when two numbers with opposite signs are added, you subtract the smaller number from the larger number, and the answer has the sign of the larger number, we get:
-6 1/2 + 3 1/4 = -3 1/4
This is because when you subtract 3 1/4 from 6 1/2, you get 3 1/4, and since the larger number in absolute value is negative, the result is also negative.