Multiple choice

Out of the four numbers, the average of the first three is 16 and that of the last three is 15. If the last number is 20 then the first number is- चार संख्याओं में से, पहली तीन का औसत 16 है और अन्तिम तीन का औसत 15 है। यदि अन्तिम संख्या 20 है तो पहली संख्या है-

  1. 21

  2. 23

  3. 27

  4. 25
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B Correct answer
Explanation

Let four numbers be a, b, c, d. First three: (a+b+c)/3 = 16, so a+b+c = 48. Last three: (b+c+d)/3 = 15, so b+c+d = 45. Given d = 20, subtracting equations gives a - d = 3, so a = 23. The middle terms b and c cancel out.

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