Question 1159205
c, amount of cashews
50-c, amount of peanuts

{{{120c+40(50-c)=80*50}}}

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{{{highlight(c=50((80-40)/(120-40)))}}}, easy enough to compute




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You may notice that the desired price of 80 php per kg is exactly in the middle of 40 and 120 php per kg.  The amount of each of the nuts should therefore be  25 kg of each.