Correctly 18243

Pupils have 10 points for each correctly solved task. They will be deducted 5 points for the wrong solution. After solving 20 tasks, Marian had 80 points. How many tasks did he solve correctly, and how many did not?

Correct answer:

a =  12
b =  8

Step-by-step explanation:


a+b = 20
10a-5b=80

a+b = 20
10·a-5·b=80

a+b = 20
10a-5b = 80

Pivot: Row 1 ↔ Row 2
10a-5b = 80
a+b = 20

Row 2 - 1/10 · Row 1 → Row 2
10a-5b = 80
1.5b = 12


b = 12/1.5 = 8
a = 80+5b/10 = 80+5 · 8/10 = 12

a = 12
b = 8

Our linear equations calculator calculates it.



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