First number is f
Second number is s
f-s=.7
f+s=1
Using elimination, you could solve this.
-1(f-s=.7); eliminate the first number.
-f+s= -.7
f+s=1
2s=.3
s=.15
Now find the second number by plugging it in:
.15+s=1
1-.15=.85
The numbers are .15 and .85.
(x cookies) / (23 students - (12/2) students) = 2 cookies per student
[x / (23 - 6)] cookies per student = 2 cookies per student
23 students * (2 cookies per students) - 12 cookies = x cookies
The "students" unit cancels
46 cookies - 12 cookies = x cookies
x cookies = 34 cookies
The first option is

The second option is

So, neither of them is equivalent to 
Answer:
1/2
Step-by-step explanation:
7/10 - 2/10 = 5/10
5/10 simplifies to 1/2 by dividing numerator and denominator by 5.