Question 906376
The other tutor Alan is correct. He knows some neat shortcuts.
Here is the proof.
a+b=960,
0.7*a+0.3*b=0.5*960
a=960-b
0.7*(960-b)+0.3*b=480
672-0.7b+0.3*b=480
-0.4*b=-192
b=480
a=960-b
a=480 mL at 0.7% b=480 mL at 0.3%
check
0.7*480+0.3*480=0.5*960
336+144=480
480=480
ok