Coffee

Coffee merchant has coffee robusta and arabica species. 1 kg Robusta is worth 450 CZK, Arabica 1 kg is 300 CZK more expensive. Calculate how many kilograms of Robusta and Arabica will need to produce 30 kg of the mixture so that the mixture costs 490 CZK per 1 kg.

Correct answer:

r =  26 kg
a =  4 kg

Step-by-step explanation:


r+a = 30
450r+(450+300)a = 30·490

r+a = 30
450·r+(450+300)·a = 30·490

a+r = 30
750a+450r = 14700

Pivot: Row 1 ↔ Row 2
750a+450r = 14700
a+r = 30

Row 2 - 1/750 · Row 1 → Row 2
750a+450r = 14700
0.4r = 10.4


r = 10.4/0.4 = 26
a = 14700-450r/750 = 14700-450 · 26/750 = 4

a = 4
r = 26

Our linear equations calculator calculates it.



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