Multiple choice

There are 12 consecutive numbers. The average of the first 6 is 19. What is the average of the last 6 numbers?

  1. 19

  2. 20

  3. 25

  4. 30

  5. 35
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let the numbers be a, a+1, ..., a+11. The first 6 have average a + 2.5 = 19, so a = 16.5. The last 6 are a+6, ..., a+11, with average a + 8.5 = 16.5 + 8.5 = 25.

AI explanation

The sum of the first 6 consecutive numbers is 6 multiplied by 19, which equals 114. Let the first number be x; then the sum of the first six is x plus (x plus 1) plus (x plus 2) plus (x plus 3) plus (x plus 4) plus (x plus 5), which equals 6x plus 15. Setting this equal to 114 gives 6x equals 99, so x equals 16.5; the last six numbers start from x plus 6, which is 22.5, and since they are also six consecutive numbers, their average is their middle point, (22.5 plus 27.5) divided by 2, equaling 25. The result is C.

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