Determine 3277

Seventh, eighth, and ninth graders were sitting in the cinema hall. There were a total of 250 pupils in the cinema hall. There were 30 more sevens than eights and ten fewer eights than nines. Determine how many pupils there were.

Correct answer:

a =  100
b =  70
c =  80

Step-by-step explanation:


a+b+c=250
a=30+b
b = c-10

a+b+c = 250
a-b = 30
b-c = -10

Row 2 - Row 1 → Row 2
a+b+c = 250
-2b-c = -220
b-c = -10

Row 3 - 1/-2 · Row 2 → Row 3
a+b+c = 250
-2b-c = -220
-1.5c = -120


c = -120/-1.5 = 80
b = -220+c/-2 = -220+80/-2 = 70
a = 250-b-c = 250-70-80 = 100

a = 100
b = 70
c = 80

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