Multiple choice

Four numbers are written in a row. The average of the first two numbers is 7, the average of the middle two terms is 2.3 and the average of the last two numbers is 8.4. The average of the first number and the last number is:

  1. 5.9

  2. 10.7

  3. 13.1

  4. Cannot be determined

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let numbers be a, b, c, d. (a+b)/2 = 7 -> a+b = 14. (b+c)/2 = 2.3 -> b+c = 4.6. (c+d)/2 = 8.4 -> c+d = 16.8. We need (a+d)/2. From equations: a+d = (a+b) + (c+d) - (b+c) = 14 + 16.8 - 4.6 = 26.2. Average = 26.2 / 2 = 13.1.

AI explanation

Let the four numbers be a, b, c and d; the sums are a plus b equals 14, b plus c equals 4.6, and c plus d equals 16.8. Adding the first and third equations gives a plus b plus c plus d equals 30.8. Subtracting the second equation, b plus c equals 4.6, from this total leaves a plus d equals 26.2. Dividing 26.2 by 2 gives the average of the first and last numbers, which is 13.1. The result is C.

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