Multiple choice

The average of first four of five numbers is 26 and that of the last four is 25. The difference between the last number and the first number is

  1. 1

  2. 4

  3. 5

  4. 16
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B Correct answer
Explanation

Let the five numbers be a, b, c, d, e. Average of first four: (a+b+c+d)/4 = 26, so a+b+c+d = 104. Average of last four: (b+c+d+e)/4 = 25, so b+c+d+e = 100. Subtracting: (a+b+c+d) - (b+c+d+e) = 104 - 100, giving a - e = 4. Therefore e - a = -4, meaning the last number is 4 less than the first number.

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