Question 904747
1*x+0.35*2=0.5(2+x)
1*x+0.7=1+0.5x
1x-0.5x=1-0.7
0.5x=0.3
x=0.6 gal of 100% is added to 2 gal of 35%  to get  2.6 gal  at 50%
check
1*0.6+0.35*2=0.5(2+0.6)
0.6+0.7=0.5(2.6)
1.3=1.3
ok