Linear Equations in One Variable

Original: $0.20 a + 0.50 b = 0.35 V$ with $a + b = V$, so $0.20 V + 0.30 b = 0.35 V$ → $b = 0.5 V$, $a = 0.5 V$. Acid amount: $0.35 V$. After adding 10 L of 20%: total acid $= 0.35 V + 2$, total volume $= V + 10$, concentration $= 0.30$: $0.35 V + 2 = 0.30(V + 10)$ → $0.05 V = 1$ → $V = 20$. Hmm, that gives 20 not 30. Recheck: $0.35V + 2 = 0.3V + 3$ → $0.05V = 1$ → $V = 20$. So answer is 20 (index 0). Adjusting answer index to 0.