Use distributive property
-28y+8y= -20y
Let 
be the number of liters of the 10% solution she needs to use. She'd end up with a 6% solution with a volume of 
liters. The starting solution contains 0.04*9 = 0.36 liter of salt. Each liter of the 10% solution contributes 0.1 liter of salt, so that
Solve for :
so Mayra needs to add 4.5 liters of the 10% solution.
To answer this question, we would use the combination formula which is
nCr, where n is the the number of objects and r is the sample.
So n would be 10, and r would be 4, since that is what we need to group.
<span>10 choose 4 is written 10C4, or C(10,4), and equals 10!/(4!(10-4)!)=10!/(4!6!)=10*9*8*7/(1*2*3*4) = 210</span>
