Question 1041460
Same as simple two part mixture problem.


u  how much cheap cookies
v  how much expensive cookies


{{{system((0.80u+1.20v)/40=0.90,u+v=40)}}}



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The analysis was written as a system of two equation, in two unknown variables.  You can convert this into a single equation in one unknown, as done in the other example problem.  Look at another example demonstrating that idea:  <a href="https://www.youtube.com/watch?v=-REjxT9KCzQ">using just one unknown variable for a two-part mixture problem</a>