Multiple choice

Average weight of 15 monkeys sitting on a tree is 35 kg. Average weight of first 6 monkeys is 28 kg and the average of last 6 monkeys is 40 kg. Weight of 7th monkey is 2.32 kg more than 8th monkey and 1.15 kg less than weight of 9th monkey. Find the average weight of 7th and 9th monkey?

  1. $38.995$
  2. $39.965$
  3. $36.965$
  4. $39.665$
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B Correct answer
Explanation

Total weight = 525. First 6: 168, last 6: 240. 7th + 8th + 9th = 525 - 168 - 240 = 117. If 8th = x, then 7th = x + 2.32, 9th = x + 2.32 + 1.15 = x + 3.47. So 3x + 5.79 = 117, x = 37.07. 7th = 39.39, 9th = 40.54. Average of 7th and 9th = (39.39 + 40.54)/2 = 79.93/2 = 39.965.

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