Question 16295
Let x = amount of whipping cream at 9% (.09).  The rest of the 35 gallons is 2%, so
35-x = amount of milk at 2%.


The result is 35 gallons of 4% milk.

.09x + .02(35-x) = .04(35)
.09x + .70 - .02x = 1.40
.07x + .70 = 1.40
.07x + .70 -.70 = 1.40-.70
.07x= .70


Divide both sides by .07:
{{{(.07x)/.07 = .70/.07 = 70/7 =10}}} gallons whipping cream
{{{35 - x = 25}}} gallons 2% milk.


Check:
Does  .09(10) + .02(25) = .04(35)
      .9 + .5 = 1.4 
It checks.


R^2 at SCC