Question 585098
.32*256+125*.20=x*(256+125)
106.92=381x
x=.28063
which is 28.063 % of 381 ml

now add 256 ml of water 
637 ml of solution
.28063*381=637x
x=.167849
16.7849 % solution of 637 ml

.167849*637+x=.55*(637+x)
add 540.596 ml pure HCL to get 55% solution