Multiple choice

If we consider four numbers, the average of first three is 18 and that of last three is 19. If the last number is 16, find the first number. यदि हम चार संख्याओं पर विचार करते हैं, तो पहले तीन का औसत 18 है और अंतिम तीन का औसत 19 है। यदि अंतिम संख्या 16 है, तो पहली संख्या ज्ञात कीजिये।

  1. 13

  2. 15

  3. 11

  4. 14
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A Correct answer
Explanation

Let numbers be a, b, c, d. Average of first three: (a+b+c)/3 = 18, so a+b+c = 54. Average of last three: (b+c+d)/3 = 19, so b+c+d = 57. Given d=16, so b+c = 57-16 = 41. Then a = 54 - (b+c) = 54 - 41 = 13. The key is using both equations to eliminate b+c.

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