School marks

Boris has a total of 22 marks. Ones have three times less than threes. There are two twos. How many have ones and threes?

Correct answer:

a =  5
c =  15

Step-by-step explanation:


a+b+c=22
b = 2
a=c/3

a+b+c = 22
b = 2
3a-c = 0

Pivot: Row 1 ↔ Row 3
3a-c = 0
b = 2
a+b+c = 22

Row 3 - 1/3 · Row 1 → Row 3
3a-c = 0
b = 2
b+1.333c = 22

Row 3 - Row 2 → Row 3
3a-c = 0
b = 2
1.333c = 20


c = 20/1.33333333 = 15
b = 2/1 = 2
a = 0+c/3 = 0+15/3 = 5

a = 5
b = 2
c = 15

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