Answer:
C1 * V1 = C2 * V2
Step-by-step explanation:
Where ‘C’ and ‘V’ refer to concentration and volume, ‘1’ and ‘2’ to solution 1 and 2 respectively. So, if ‘1’ refers to the HCl solution, we want to solve this equation for C1.
V1 = (C2*V2)/C1 = (0.4 * 50)/40 = 0.5 M