Question 192099
total is  55  gal

at  30%,  solute  is  30% 0f 55  or  .3*55=  16.5  gal

required  to  have  50%  of  55  =  .50*55=  27.5  gal


16.5  -  .3x  +1.00x  = 27.5

subt  16.5  both  sides  and  simplify

(1-.3)x= 11

.7x  = 11

divide  by  .7

x=15.714    or  in  sig  fig  (16)   ANSWER

checking
.3*15.714 =  4.714

16.5 - 4.714+15.714 = 27.5     ok