Question 156024
Here are the rules.  If you see TWO signs next to each other, use the following rules to change both to a single sign:
+ + replace with +
+ - replace with -
- + replace with -
- - replace with +
.
Same thing when MULTIPLYING:
+ + is a +
+ - is a -
- + is a -
- - is a +
.
Looking at your problems:
10+(-4)
I see a + - together -- replace with a -
10-4
= 6
.
-2(-6)
Multiplying - and - becomes a +
= 12
.
-7+7 = 0
.
-0.25-4= -4.25
.
-5+23 = 18
.
-15+(-9) 
Replace + - with a -
-15-9 = -24