Multiple choice

Fernandez owns a bookshop. The average number of books he sold is 75 for y number of days. If today he sells a total of 120 books and his average increases to 90 books, what the number of days for which the average is 75?

  1. 1

  2. 2

  3. 3

  4. 4

  5. 5
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B Correct answer
Explanation

Let y be the number of days. Total books = 75y. New total = 75y + 120. New average = (75y + 120) / (y + 1) = 90. 75y + 120 = 90y + 90. 15y = 30, y = 2.

AI explanation

Let y be the number of days the average was 75. Using the overall average formula, the total books sold over those days is 75y, and after selling 120 books today, the new total becomes 75y + 120. The new average is calculated over (y + 1) days, so (75y + 120) / (y + 1) = 90. Solving for y gives 75y + 120 = 90y + 90, which simplifies to 15y = 30, resulting in y = 2. The average was 75 for 2 days.

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