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.