Three-day 7522

Pupils walked a total of 30 km during the three-day trip. On the first day, they ran twice as much as on the third day, and on the second day, they ran 6 km more than on the third day. How many km have they traveled each day?

Correct answer:

a =  12
b =  12
c =  6

Step-by-step explanation:


a+b+c=30
a = 2c
b = 6+c

a+b+c=30
a = 2·c
b = 6+c

a+b+c = 30
a-2c = 0
b-c = 6

Row 2 - Row 1 → Row 2
a+b+c = 30
-b-3c = -30
b-c = 6

Row 3 + Row 2 → Row 3
a+b+c = 30
-b-3c = -30
-4c = -24


c = -24/-4 = 6
b = -30+3c/-1 = -30+3 · 6/-1 = 12
a = 30-b-c = 30-12-6 = 12

a = 12
b = 12
c = 6

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