Question 994483
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If all students are sophomores or juniors:
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J=number of juniors; S=number of sophomores=J+18
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J+S=78
J+J+18=78
2J=60
J=30
ANSWER 1: There are 30 juniors in the class.
S=J+18=30+18=48
ANSWER 2: There are 48 sophomores in the class.
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CHECK:
J+S=78
30+48=78
78=78