A student's first three test scores are 80, 75, and 90. What score must the student earn on the fourth test to average exactly 85?

To average 85 over four tests, the total of all four scores must be 4 × 85 = 340. Current total: 80 + 75 + 90 = 245. Required fourth score: 340 - 245 = 95. Verification: (80 + 75 + 90 + 95) ÷ 4 = 340/4 = 85 ✓. This 'find the missing value to achieve an average' problem appears regularly on the ASVAB. Strategy: (1) Calculate the required total = desired average × number of values; (2) Sum the known values; (3) Subtract to find the missing value. Variations include: 'How many points above/below the average is this score?' (compute score - average for each value). 'If a score is dropped from the average, what is the new average?' (subtract the dropped score from the sum, divide by the new count). Always check: does the missing value make sense in context? (Some problems require values within a possible range, like 0-100 for test scores.)