Question 1101669
Let A denote the 95% solution and B denote the 80% solution which we have.
Let C denote the 90% solution which we want.
Using the method of alligation.
10= 90 - 80
5= 95 - 90
E.g. There are 10 parts of A plus 5 parts of B
Then 10+5=15 parts total
10/15=0.66666667
0.66666667*15=10
10 gal of 95% solution.

15 gal-10 gal=5 gal
5 gal of 80% solution.
or
5/15=0.33333333
0.33333333*15=5 gal
5 gal of 80% solution.
check
0.8 * 5 + 0.95 * 10 = 0.9*15
4.0 + 9.5 = 13.5
13.5 = 13.5
ok