Multiple choice

The average of some natural numbers is 15. If 30 is added to first number and 5 is subtracted from the last number, the average become 17.5. then the numbers of natural numbers is : কিছু বাস্তব সংখ্যার গড় 15,যদি প্রথম সংখ্যার সাথে 30 যোগ করা হয় এবং শেষ সংখ্যা থেকে 5 বিয়োগ করা হয় তাহলে গড় দাঁড়ায় 17.5, কতগুলি সংখ্যা ছিল?

  1. 12

  2. 15

  3. 10

  4. 11
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C Correct answer
Explanation

Let there be n numbers. Their original sum is 15n, and the changed sum is 15n + 30 - 5 = 15n + 25. Since the new average is 17.5, 15n + 25 = 17.5n, giving n = 10.

AI explanation

The total increase in the sum of the numbers is 30 added to the first number and 5 subtracted from the last, resulting in a net increase of 25. The average increases by 2.5, rising from 15 to 17.5. Using the formula that the number of items equals the total increase divided by the average increase, we calculate 25 divided by 2.5, which equals 10.

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