Multiple choice

The average age of a group of 10 students was 15 years. When 5 more students joined the group, the average age rose by 1 year. The average age (in years) of new students was

  1. 18 years

  2. 20 years

  3. 16 years

  4. 15 years

  5. 21 years
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A Correct answer
Explanation

Initial sum = 10 * 15 = 150. New sum = 15 * 16 = 240. Sum of 5 new students = 240 - 150 = 90. Average = 90 / 5 = 18.

AI explanation

The total age of the initial 10 students is 10 multiplied by 15, equaling 150 years. After 5 new students join, the total age for all 15 students becomes 15 multiplied by 16, which is 240 years. The total age of just the 5 new students is 240 minus 150, giving 90 years; dividing 90 by 5 yields an average age of 18 years for the new students.

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