Question 884849
Assume the resulting mixture 4% cream is 100 units quantity of mixture.
x is quantity of 2% cream
y is quantity of 5% cream


(2x+5y)/100=4 and x+y=100 correspondingly for concentration and for sum of parts.



2x+5y=400
and
x+y=100


The numbers allow for fairly easy use of Elimination Method to start.
2x+5y=400
and
2x+2y=200
-
-
3y=200
y=66.7 approximately, but theoretically {{{66&2/3}}} units.
Meaning, {{{x=33&1/3}}} parts.
That would be for 100 units of finished 4% cream mixture.


<b>Simpler meaning is, 1 part of 2% cream and 2 parts of the 5% cream.</b>