Multiple choice

The average of $25$ results is $18$. The average of first twelve of them is 14 and of last twelve is $17$. Find the thirteenth result.

  1. $80$
  2. $79$
  3. $78$
  4. $77$
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C Correct answer
Explanation

Total sum of 25 results = 25 * 18 = 450. Sum of first 12 = 12 * 14 = 168. Sum of last 12 = 12 * 17 = 204. The 13th result = 450 - (168 + 204) = 450 - 372 = 78.

AI explanation

The total sum of all 25 results is 25 multiplied by 18, which equals 450. The sum of the first twelve results is 12 multiplied by 14, equaling 168, and the sum of the last twelve results is 12 multiplied by 17, equaling 204. The combined sum of these 24 results is 168 plus 204, giving 372. The thirteenth result is the total sum minus this combined sum, so 450 minus 372 equals 78.

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