At least 89
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Set up the equation:
- (67 + 88 + 96 + x) / 4 ≥ 85,
where x is the score on the fourth test
Solving this inequality, we get:
- 251 + x ≥ 85*4
- 251 + x ≥ 340
- x ≥ 340 - 251
- x ≥ 89
Therefore, the student must score at least 89 on the fourth test.
