Multiple choice

The average (arithmetic mean) production at a factory was 60 units per day over the past n days. If today's production of 120 units increases the average to 65 units per day, what is the value of n?

  1. 9

  2. 11

  3. 12

  4. 15

  5. 16
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Total units over n days is 60n. After adding 120 units on day n+1, the total is 60n + 120, and the new average is (60n + 120)/(n + 1) = 65. Solving 60n + 120 = 65n + 65 gives 5n = 55, so n = 11.

AI explanation

Using the average formula, the total production for n days is 60n. Adding today's production makes the total 60n + 120, and dividing by the new total of days (n + 1) gives the new average of 65. Setting up the equation (60n + 120) / (n + 1) = 65 and solving yields 60n + 120 = 65n + 65, which means 5n = 55, so n equals 11.

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