Edward C. answered 04/13/15
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Caltech Grad for math tutoring: Algebra through Calculus
Let C = kg of cashews
Let P = kg of pecans
10 kg mix ==> C + P = 10 ==> C = 10 - P
The total value of a mixture of C kg of cashews and P kg of pecans is 8*C + 9*P
The total value of a 10 kg mix which sells for 8.40/kg is 10*8.4 = 84
So 8*C + 9*P = 84
Substitute the value for C from the 1st equation into this equation
8*(10 - P) + 9*P = 84
80 - 8*P + 9*P = 84
P = 4
So C = 10 - 4 = 6
There should be 6 kg of cashews and 4 kg of pecans in the mix
Check: (6 kg)*($8 / kg) + (4 kg)*($9 / kg) = $48 + $36 = $84 = $8.40 / kg for a 10 kg mix