Mixing water

We should fill the 30-liter container with water at 60 degrees Celsius. How many liters of water 80 degrees C hot, and how many liters of water 20 degrees Celsius warm we have to mix?

Correct answer:

a =  20
b =  10

Step-by-step explanation:


a+b = 30
80a + 20b = 60·(a+b)

a+b = 30
80·a + 20·b = 60·(a+b)

a+b = 30
20a-40b = 0

Pivot: Row 1 ↔ Row 2
20a-40b = 0
a+b = 30

Row 2 - 1/20 · Row 1 → Row 2
20a-40b = 0
3b = 30


b = 30/3 = 10
a = 0+40b/20 = 0+40 · 10/20 = 20

a = 20
b = 10

Our linear equations calculator calculates it.



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