A student has scores of 60, 70, and 80 in three tests. If he wants an average of 75 after the fourth test, what score does he need?

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Q: A student has scores of 60, 70, and 80 in three tests. If he wants an average of 75 after the fourth test, what score does he need?

Solution: Let the fourth score be x. (60 + 70 + 80 + x) / 4 = 75 => 210 + x = 300 => x = 90.

Steps: 10

Step 1: Add the scores of the first three tests: 60 + 70 + 80.
Step 2: Calculate the total from Step 1: 60 + 70 + 80 = 210.
Step 3: Let the score of the fourth test be x.
Step 4: To find the average of four tests, use the formula: (Total of all scores) / 4 = Average.
Step 5: Set up the equation: (210 + x) / 4 = 75.
Step 6: Multiply both sides of the equation by 4 to eliminate the fraction: 210 + x = 75 * 4.
Step 7: Calculate 75 * 4: 75 * 4 = 300.
Step 8: Now the equation is: 210 + x = 300.
Step 9: Subtract 210 from both sides to solve for x: x = 300 - 210.
Step 10: Calculate 300 - 210: x = 90.