Question 1022504
Ten pints of 40% acid means 10*0.40 = 4 pints of the mixture is alcohol.
Ten pints of 80% acid means 10*0.80 = 8 pints of the mixture is alcohol.

==> The new mixture of 10+10 = 20 pints has 4+8 = 12 pints of alcohol in it.
The new mixture is {{{(12/20)*100}}}% = 60% alcohol.