Final answer:
The value of the given mathematical expression -0.25 - (-15) + 0.3 + (-24) is calculated by correctly adding and subtracting positive and negative numbers, resulting in -8.95.
Step-by-step explanation:
The value of the expression -0.25 - (-15) + 0.3 + (-24) can be determined by understanding the rules for adding and subtracting positive and negative numbers. When we subtract a negative number, it is the same as adding its positive counterpart.
First, replace the subtraction of a negative with an addition:
-0.25 + 15 + 0.3 - 24
Now, combine the like terms; add the positive numbers and the negative numbers separately:
(-0.25 + 0.3) + (15 - 24)
The result is:
0.05 + (-9)
Finally, add the remaining terms:
0.05 - 9 = -8.95
Hence, the value of the expression is -8.95.