Question 269893
This is a mixture problem. Here is a table based on the given information.
solutions . . . . . . . . . % . . . . . . . . . .. gallon . . . . . . . . .. . %-gallon
70% . . . . . . . . . . . . .70. . . . . . . . . . . g. . . . . . . . . . . . . . .70g
40%. . . . . . . . . . . . . 40. . . . . . . . . . . 90 - g . . . . . . . . . . .3600 - 40g
mixture. . . . . . . . . . 50. . . . . . . . . . . 90 . . . . . . . . . . . . . .4500
From column 3 we get
{{{70g + 3600 - 40g = 4500}}
simplify to get
{{{30g + 3600 = 4500}}}
subtract to get
{{{30g = 900}}}
divide to get
 {{{g = 30}}}
----------
you will need 30 gallons of 70% and 60 gallons of 40%.