Two-fifths 7764

No one got a grade worse than three. A third of the class got one, two-fifths two, and eight students had three. How many students had one or two?

Correct answer:

a =  10
b =  12

Step-by-step explanation:


n/3 + 2/5 n + 8 =n
a = n/3
b = 2/5n

n/3 + 2/5·n + 8 =n
a = n/3
b = 2/5·n

4n = 120
3a-n = 0
5b-2n = 0

Pivot: Row 1 ↔ Row 2
3a-n = 0
4n = 120
5b-2n = 0

Pivot: Row 2 ↔ Row 3
3a-n = 0
5b-2n = 0
4n = 120


n = 120/4 = 30
b = 0+2n/5 = 0+2 · 30/5 = 12
a = 0+n/3 = 0+30/3 = 10

a = 10
b = 12
n = 30

Our linear equations calculator calculates it.
b=12



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