An organizer is planning a wedding party and stipulates that the fruit punch be 20% concentrate. Ryan and Noel will both bring homemade fruit punch. Ryan’s punch will be 10% concentrate and Noel’s 35%. If together they can bring 15 liters of punch, how many liters should Ryan bring?

9 liters

Step-by-step explanation:

it is really easy, you have Ryan's liters + Noel liters = 15 liters

so, the same:

x + y  = 15

y = 15 - x

and you need the value of "x"

in the formula C1*V1 + C1*V2 = Cf*Vf

it is:

10%*X + 35%*Y = 20%*15

and we use the value of Y:

0.1*X + 0.35*(15 - X) = 0.2*15

so

0.1*X + 5.25 - 0.35X = 3

0.1X - 0.35X = 3 - 5.25

-0.25X = -2.25

X = 2.25/0.25

X= 9

:D

When the coefficient of X is positive!